Lightstreamer Web Client

https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/
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### Install Lightstreamer Web Client via npm

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/index.html

Use this command to install the Lightstreamer Web Client package using npm. This package provides various library formats compatible with module bundlers and AMD loaders.

```bash
npm install lightstreamer-client-web
```

--------------------------------

### Complete HTML Page Example

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/index.html

A full HTML page demonstrating the Lightstreamer client connection, subscription, and update handling. Includes the necessary script tag for the Lightstreamer library.

```html
<html>
<head>
    <script src="https://unpkg.com/lightstreamer-client-web/lightstreamer.min.js"></script>
    <script>
    var client = new Ls.LightstreamerClient("https://push.lightstreamer.com","DEMO");  
    client.connect();
    
    var sub = new Ls.Subscription("MERGE",["item1","item2","item3"],["stock_name","last_price"]);
    sub.setDataAdapter("QUOTE_ADAPTER");
    sub.setRequestedSnapshot("yes");
    sub.addListener({
        onItemUpdate: function(obj) {
          console.log(obj.getValue("stock_name") + ": " + obj.getValue("last_price"));
        }
    });
    client.subscribe(sub);
    </script>
</head>
<body>
</body>
</html>

```

--------------------------------

### Handle Item Updates

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/index.html

Attach a listener to a Subscription to process incoming data updates. This example logs the stock name and last price for each update.

```javascript
sub.addListener({
    onItemUpdate: function(obj) {
      console.log(obj.getValue("stock_name") + ": " + obj.getValue("last_price"));
    }
});

```

--------------------------------

### getRealMaxBandwidth

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the maximum bandwidth that can be consumed for the data coming from Lightstreamer Server.

```APIDOC
## getRealMaxBandwidth()

### Description
Inquiry method that gets the maximum bandwidth that can be consumed for the data coming from Lightstreamer Server. This is the actual maximum bandwidth, in contrast with the requested maximum bandwidth, returned by ConnectionOptions#getRequestedMaxBandwidth. The value may differ from the requested one because of restrictions operated on the server side, or because bandwidth management is not supported (in this case it is always "unlimited"), but also because of number rounding.

**Lifecycle:** If a connection to Lightstreamer Server is not currently active, null is returned; soon after the connection is established, the value becomes available, as notified by a call to ClientListener#onPropertyChange with argument "realMaxBandwidth".

### See:
* ConnectionOptions#setRequestedMaxBandwidth

### Returns:
A decimal number, which represents the maximum bandwidth applied by the Server for the streaming or polling connection expressed in kbps (kilobits/sec), or the string "unlimited", or null. (Number | String)
```

--------------------------------

### getFirstRetryMaxDelay

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the maximum time to wait before trying a new connection to the Server in case the previous one is unexpectedly closed while correctly working.

```APIDOC
## getFirstRetryMaxDelay()

### Description
Inquiry method that gets the maximum time to wait before trying a new connection to the Server in case the previous one is unexpectedly closed while correctly working.

### See:
* ConnectionOptions#setFirstRetryMaxDelay

### Returns:
The max time (in milliseconds) to wait before trying a new connection. (Number)
```

--------------------------------

### getStatus()

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnDevice.html

Gets the current status of the MPN device. The status can be UNKNOWN, REGISTERED, or SUSPENDED, indicating the device's registration and suspension state on the server.

```APIDOC
## getStatus()

### Description
Retrieves the status of the device. The status can be:
  * `UNKNOWN`: when the MPN device object has just been created or deleted. In this status MpnDevice#isRegistered and MpnDevice#isSuspended are both false.
  * `REGISTERED`: when the MPN device object has been successfully registered on the server. In this status MpnDevice#isRegistered is true and MpnDevice#isSuspended is false.
  * `SUSPENDED`: when a server error occurred while sending push notifications to this MPN device and consequently it has been suspended. In this status MpnDevice#isRegistered and MpnDevice#isSuspended are both true.

### Method
`getStatus()`

### Returns
- **String**: The status of the device.
```

--------------------------------

### getForcedTransport

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the value of the forced transport (if any).

```APIDOC
## getForcedTransport()

### Description
Inquiry method that gets the value of the forced transport (if any).

### See:
* ConnectionOptions#setForcedTransport

### Returns:
The forced transport or null (String)
```

--------------------------------

### Create and Connect Lightstreamer Client

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/index.html

Instantiate a LightstreamerClient and establish a connection to the server. Ensure the server URL and client ID are correctly specified.

```javascript
var client = new LightstreamerClient("https://push.lightstreamer.com/","DEMO");
client.connect();

```

--------------------------------

### getPollingInterval

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the polling interval used for polling connections.

```APIDOC
## getPollingInterval()

### Description
Inquiry method that gets the polling interval used for polling connections. If the value has just been set and a polling request to Lightstreamer Server has not been performed yet, the returned value is the polling interval that is being requested to the Server. Afterwards, the returned value is the the time between subsequent polling requests that is really allowed by the Server, that may be different, because of Server side constraints.

### See:
* ConnectionOptions#setPollingInterval

### Returns:
The time (in milliseconds) between subsequent polling requests. (Number)
```

--------------------------------

### getNodeTypes()

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/DynaGrid.html

Gets the list of node types that would be searched in case of a call to AbstractGrid#parseHtml.

```APIDOC
## getNodeTypes()

### Description
Inquiry method that gets the list of node of types that would be searched in case of a call to AbstractGrid#parseHtml.

Inherited From:
    
  * AbstractGrid#getNodeTypes

### Returns
a list of node type names.

Type
     Array.<String>
```

--------------------------------

### Create a Subscription

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/index.html

Define a Subscription for data, specifying the mode, items, and fields. Set the data adapter and request a snapshot if needed.

```javascript
var sub = new Ls.Subscription("MERGE",["item1","item2","item3"],["stock_name","last_price"]);
sub.setDataAdapter("QUOTE_ADAPTER");
sub.setRequestedSnapshot("yes");
client.subscribe(sub);

```

--------------------------------

### getHttpExtraHeaders

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the JSON object containing the extra headers to be sent to the server.

```APIDOC
## getHttpExtraHeaders()

### Description
Inquiry method that gets the JSON object containing the extra headers to be sent to the server.

### See:
* ConnectionOptions#setHttpExtraHeaders

### Returns:
the JSON object containing the extra headers to be sent (Object)
```

--------------------------------

### connect()

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/LightstreamerClient.html

Initiates a connection to the Lightstreamer Server. It manages the 'Stream-Sense' mechanism, automatically switching to polling if streaming is unavailable or delayed. It's recommended to call this as a final step in page initialization.

```APIDOC
## connect()

### Description
Operation method that requests to open a Session against the configured Lightstreamer Server.
When connect() is called, unless a single transport was forced through ConnectionOptions#setForcedTransport, the so called "Stream-Sense" mechanism is started: if the client does not receive any answer for some seconds from the streaming connection, then it will automatically open a polling connection.
A polling connection may also be opened if the environment is not suitable for a streaming connection.
When connect() is used to activate the Lightstreamer Session on page start up, it is suggested to make this call as the latest action of the scripts in the page. Otherwise, if the stream connection is opened but third-party scripts are consuming most of the CPU for page initialization (initial rendering, etc.), the parsing of the streaming response could be delayed to the point that the Client switches to polling mode. This is usually not the case nowadays but may still happen if the client is used on old machines.
Note that as "polling connection" we mean a loop of polling requests, each of which requires opening a synchronous (i.e. not streaming) connection to Lightstreamer Server.

**Lifecycle:** Note that the request to connect is accomplished by the client asynchronously; this means that an invocation to LightstreamerClient#getStatus right after connect() might not reflect the change yet. Also if a CPU consuming task is performed right after the call the connection will be delayed.
When the request to connect is finally being executed, if the current status of the client is not DISCONNECTED, then nothing will be done.

### Parameters
#### Path Parameters
- **listener** (ClientListener) - Required - An object that will receive the events as shown in the ClientListener interface. Note that the given instance does not have to implement all of the methods of the ClientListener interface. In fact it may also implement none of the interface methods and still be considered a valid listener. In the latter case it will obviously receive no events.

### Throws
- **IllegalStateException** - if no server address was configured and there is no suitable default address to be used.

### See Also
- LightstreamerClient#getStatus
- LightstreamerClient#disconnect
- ClientListener#onStatusChange
- ConnectionDetails#setServerAddress
```

--------------------------------

### SafariMpnBuilder Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/SafariMpnBuilder.html

Initializes a new SafariMpnBuilder instance. This can be done with an optional JSON structure representing a push notification format.

```APIDOC
## new SafariMpnBuilder(notificationFormat)

### Description
Creates an object to be used to create a push notification format. Use setters methods to set the value of push notification fields or use a JSON structure to initialize the fields.

### Parameters
* `notificationFormat` (object, optional) - A JSON structure representing a push notification format.

### See Also
* MpnSubscription#setNotificationFormat
```

--------------------------------

### getContentLength

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the length expressed in bytes to be used by the Server for the response body on a HTTP stream connection.

```APIDOC
## getContentLength()

### Description
Inquiry method that gets the length expressed in bytes to be used by the Server for the response body on a HTTP stream connection.

### Returns:
* the length to be used by the Server for the response body on a HTTP stream connection (Number)
```

--------------------------------

### LightstreamerClient Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/LightstreamerClient.html

Creates a LightstreamerClient instance to manage communication with a Lightstreamer Server. Multiple clients can be instantiated.

```APIDOC
## new LightstreamerClient(serverAddress, adapterSet)

### Description
Creates an object to be configured to connect to a Lightstreamer server and to handle all the communications with it. It is possible to instantiate as many LightstreamerClient as needed. Each LightstreamerClient is the entry point to connect to a Lightstreamer server, subscribe to as many items as needed and to send messages.

### Parameters
#### Path Parameters
- **serverAddress** (String) - Optional - The address of the Lightstreamer Server to which this LightstreamerClient will connect to. It is possible not to specify it at all or to specify it later. See ConnectionDetails#setServerAddress for details.
- **adapterSet** (String) - Optional - The name of the Adapter Set mounted on Lightstreamer Server to be used to handle all requests in the Session associated with this LightstreamerClient. It is possible not to specify it at all or to specify it later. See ConnectionDetails#setAdapterSet for details.

### Throws
- IllegalArgumentException: if a not valid address is passed. See ConnectionDetails#setServerAddress for details.
```

--------------------------------

### setRootNode

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/StaticGrid.html

Specifies the root DOM node to be used as the starting point for searching grid cells. Only descendants of this node will be considered.

```APIDOC
## setRootNode(rootNode)

### Description
Setter method that specifies the root node to be used when searching for grid cells. If specified, only descendants of the supplied node will be checked. Anyway note that if nodes are explicitly set through the constructor or through the StaticGrid#addCell method, then the search will not be performed at all.

### Parameters
#### Path Parameters
* **rootNode** (Object) - Required - a DOM node to be used as starting point when searching for grid cells.
```

--------------------------------

### getKeepaliveInterval

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the interval between two keepalive packets sent by Lightstreamer Server on a stream connection when no actual data is being transmitted.

```APIDOC
## getKeepaliveInterval()

### Description
Inquiry method that gets the interval between two keepalive packets sent by Lightstreamer Server on a stream connection when no actual data is being transmitted. If the value has just been set and a connection to Lightstreamer Server has not been established yet, the returned value is the time that is being requested to the Server. Afterwards, the returned value is the time used by the Server, that may be different, because of Server side constraints. If the returned value is 0, it means that the interval is to be decided by the Server upon the next connection.

### See:
* ConnectionOptions#setKeepaliveInterval

### Returns:
The time, expressed in milliseconds, between two keepalive packets sent by the Server, or 0. (Number)
```

--------------------------------

### onListenStart()

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/StatusWidget.html

Event handler called when the StatusWidget is added to a LightstreamerClient.

```APIDOC
## onListenStart()

### Description
Event handler that receives a notification when the ClientListener instance is added to a LightstreamerClient through LightstreamerClient#addListener. This is the first event to be fired on the listener.

### Overrides
- ClientListener#onListenStart
```

--------------------------------

### getStatus

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/LightstreamerClient.html

Gets the current status of the Lightstreamer client and the transport protocol being used, if applicable. The status indicates the connection state and activity of the client.

```APIDOC
## getStatus()

### Description
Inquiry method that gets the current client status and transport (when applicable).

### Returns
- String - The current client status. It can be one of the following values:
  * "CONNECTING"
  * "CONNECTED:STREAM-SENSING"
  * "CONNECTED:WS-STREAMING"
  * "CONNECTED:HTTP-STREAMING"
  * "CONNECTED:WS-POLLING"
  * "CONNECTED:HTTP-POLLING"
  * "STALLED"
  * "DISCONNECTED:WILL-RETRY"
  * "DISCONNECTED:TRYING-RECOVERY"
  * "DISCONNECTED"
```

--------------------------------

### DynaGridListener Methods

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/DynaGridListener.html

This section details the methods available for implementing the DynaGridListener interface.

```APIDOC
## onCurrentPagesChanged(numPages)

### Description
Event handler that receives the notification that the number of logical pages has changed. The number of logical pages can grow or shrink because of addition or removal of rows and because of changes in the logical page size setting. By implementing this method it is possible, for example, to implement a dynamic page index to allow direct jump to each logical page.

### Parameters
#### Path Parameters
- **numPages** (Number) - Required - The current total number of logical pages.

### See Also
- DynaGrid#setMaxDynaRows
- DynaGrid#goToPage
```

```APIDOC
## onVisualUpdate(key, visualUpdate, domNode)

### Description
Event handler that is called by Lightstreamer each time a row of the grid is being added or modified. By implementing this method, it is possible to perform custom formatting on the field values, to set the cells stylesheets and to control the display policy. In addition, through a custom handler, it is possible to perform custom display actions for the row, by directly acting on the DOM element containing the grid row. This event is also fired when a row is being removed from the grid, to allow clearing actions related to custom display actions previously performed for the row. Row removal may happen when the DynaGrid is listening to events from Subscription instance(s), and the first Subscription it listens to is a COMMAND Subscription; removal may also happen in case of AbstractWidget#removeRow or AbstractWidget#clean execution and in case of destruction of a row caused by exceeding the maximum allowed number of rows (see DynaGrid#setMaxDynaRows). This event is fired before the update is applied to both the HTML cells of the grid and the internal model. As a consequence, through AbstractWidget#updateRow, it is still possible to modify the current update. This notification is unrelated to paging activity. New or changed rows are notified regardless that they are being shown in the current page or that they are currently hidden. Also, no notifications are available to signal that a row is entering or exiting the currently displayed page.

### Parameters
#### Path Parameters
- **key** (String) - Required - the key associated with the row that is being added/removed/updated (keys are described in AbstractWidget).
- **visualUpdate** (VisualUpdate) - Required - a value object containing the updated values for all the cells, together with their display settings. The desired settings can be set in the object, to substitute the default settings, before returning. visualUpdate can also be null, to notify a clearing action. In this case, the row is being removed from the page.
- **domNode** (Object) - Required - The DOM pointer to the HTML row involved. The row element has been created by Lightstreamer, by cloning the template row supplied to the DynaGrid.
```

--------------------------------

### build()

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/SafariMpnBuilder.html

Generates the final JSON string for the push notification format.

```APIDOC
## build()

### Description
Produces the JSON structure for the push notification format specified by this object.

### Returns
* String - The JSON structure for the push notification format.
```

--------------------------------

### StaticGrid Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/StaticGrid.html

Initializes a new StaticGrid instance. This object can be added to a Subscription to display data in a grid format using static HTML rows.

```APIDOC
## new StaticGrid(id, autoParse, rootEl, cells)

### Description
Creates an object that extends AbstractGrid displaying its values in a grid made of HTML elements. The grid rows are displayed into statically prepared HTML rows. The object can be supplied to Subscription#addListener and Subscription#removeListener in order to display data from one or more Subscriptions.

### Parameters
#### Parameters
- **id** (String) - An identification string to be specified in the HTML element as the data "data-grid" property value to make it possible for this StaticGrid instance to recognize its cells. The binding between the cells and the StaticGrid is performed during the AbstractGrid#parseHtml execution.
- **autoParse** (boolean) - If true the AbstractGrid#parseHtml method is executed before the constructor execution is completed. If false the parseHtml method has to be called later by custom code. It can be useful to set this flag to false if, at the time of the StaticGrid instance creation, the HTML elements designated as cells are not yet ready on the page.
- **rootEl** (Object) - if specified, the cells to make up the HTML grid will only be searched in the list of descendants of this node. Equivalent to a StaticGrid#setRootNode call, but useful if autoParse is true.
- **cells** (Array.<Object>) - an array of DOMElement instances that will make up the HTML grid for this StaticGrid instance. If specified and not empty, the parseHtml method will avoid searching cells in the DOM of the page. Equivalent to multiple StaticGrid#addCell calls, but also useful if autoParse is true.
```

--------------------------------

### getIdleTimeout

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Inquiry method that gets the maximum time the Server is allowed to wait for any data to be sent in response to a polling request, if none has accumulated at request time.

```APIDOC
## getIdleTimeout()

### Description
Inquiry method that gets the maximum time the Server is allowed to wait for any data to be sent in response to a polling request, if none has accumulated at request time. The wait time used by the Server, however, may be different, because of server side restrictions.

### See:
* ConnectionOptions#setIdleTimeout

### Returns:
The time (in milliseconds) the Server is allowed to wait for data to send upon polling requests. (Number)
```

--------------------------------

### MpnDevice Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnDevice.html

Creates an MpnDevice object to describe an MPN device for registration with the Lightstreamer Server's MPN Module. It handles automatic acquisition and saving of device tokens from localStorage to manage token changes.

```APIDOC
## new MpnDevice(token, appId, platform)

### Description
Creates an object to be used to describe an MPN device that is going to be registered to the MPN Module of Lightstreamer Server. During creation the MpnDevice tries to acquires any previously registered device token from localStorage. It then saves the current device token on localStorage. Saving and retrieving the previous device token is used to handle automatically the cases where the token changes. The MPN Module of Lightstreamer Server is able to move MPN subscriptions associated with the previous token to the new one.

### Parameters
#### Path Parameters
- **token** (String) - Required - the device token
- **appId** (String) - Required - the application identifier
- **platform** (String) - Required - either "Google" for Google's Firebase Cloud Messaging (FCM) or "Apple" for Apple Push Notification Service (APNs)

### Throws
IllegalArgumentException if `token` or `appId` is null or `platform` is not "Google" or "Apple".
```

--------------------------------

### ConnectionOptions Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Used by LightstreamerClient to provide an extra connection properties data object.

```APIDOC
## new ConnectionOptions()

### Description
Used by LightstreamerClient to provide an extra connection properties data object.

### See:
* LightstreamerClient
```

--------------------------------

### ConsoleLoggerProvider Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConsoleLoggerProvider.html

Creates an instance of the ConsoleLoggerProvider with a specified logging level.

```APIDOC
## new ConsoleLoggerProvider(level)

### Description
Creates an instance of the concrete system console logger.

### Parameters
#### Path Parameters
- **level** (number) - Required - The desired logging level. See ConsoleLogLevel.
```

--------------------------------

### MpnDeviceListener Interface

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnDeviceListener.html

The MpnDeviceListener interface is implemented to receive MPN device events. It includes handlers for the start and end of listening, registration success and failure, status changes, and suspension/resumption of the device.

```APIDOC
## MpnDeviceListener

Interface to be implemented to receive MPN device events including registration, suspension/resume and status change.

### Methods

#### onListenEnd()

Event handler called when the MpnDeviceListener instance is removed from an MPN device object through MpnDevice#removeListener. This is the last event to be fired on the listener.

#### onListenStart()

Event handler called when the MpnDeviceListener instance is added to an MPN device object through MpnDevice#addListener. This is the first event to be fired on the listener.

#### onRegistered()

Event handler called when an MPN device object has been successfully registered on the server's MPN Module. This event handler is always called before other events related to the same device. Note that this event can be called multiple times in the life of an MPN device object in case the client disconnects and reconnects. In this case the device is registered again automatically.

#### onRegistrationFailed(code, message)

Event handler called when the server notifies an error while registering an MPN device object. By implementing this method it is possible to perform recovery actions.

##### Parameters:
Name | Type | Description
---|---|---
`code` | Number | The error code sent by the Server. It can be one of the following:
  * 40 - the MPN Module is disabled, either by configuration or by license restrictions.
  * 41 - the request failed because of some internal resource error (e.g. database connection, timeout, etc.).
  * 43 - invalid or unknown application ID.
  * 45 - invalid or unknown MPN device ID.
  * 48 - MPN device suspended.
  * 66 - an unexpected exception was thrown by the Metadata Adapter while authorizing the connection.
  * 68 - the Server could not fulfill the request because of an internal error.
  * <= 0 - the Metadata Adapter has refused the subscription request; the code value is dependent on the specific Metadata Adapter implementation.
`message` | String | The description of the error sent by the Server; it can be null.

#### onResumed()

Event handler called when an MPN device object has been resumed on the server's MPN Module. An MPN device may be resumed from suspended state at the first subsequent registration. Note that in some server clustering configurations this event may not be called.

#### onStatusChanged(status, timestamp)

Event handler called when the server notifies that an MPN device changed its status. Note that in some server clustering configurations the status change for the MPN device suspend event may not be called.

##### Parameters:
Name | Type | Description
---|---|---
`status` | String | The new status of the MPN device. It can be one of the following:
  * `UNKNOWN`
  * `REGISTERED`
  * `SUSPENDED`
`timestamp` | Number | The server-side timestamp of the new device status.

See:
      
  * MpnDevice#getStatus
  * MpnDevice#getStatusTimestamp

#### onSubscriptionsUpdated()

Event handler called when the server notifies that the list of MPN subscription associated with an MPN device has been updated. After registration, the list of pre-existing MPN subscriptions for the MPN device is updated and made available through the LightstreamerClient#getMpnSubscriptions method.

See:
    
  * LightstreamerClient#getMpnSubscriptions

#### onSuspended()

Event handler called when an MPN device object has been suspended on the server's MPN Module. An MPN device may be suspended if errors occur during push notification delivery. Note that in some server clustering configurations this event may not be called.
```

--------------------------------

### Subscription Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/Subscription.html

Creates a Subscription object to describe a subscription to Lightstreamer Server. This object is used with LightstreamerClient#subscribe and LightstreamerClient#unsubscribe to manage the subscription state.

```APIDOC
## new Subscription(subscriptionMode, itemsopt, fieldsopt)

### Description
Creates an object to be used to describe a Subscription that is going to be subscribed to through Lightstreamer Server. The object can be supplied to LightstreamerClient#subscribe and LightstreamerClient#unsubscribe, in order to bring the Subscription to "active" or back to "inactive" state.
Note that all of the methods used to describe the subscription to the server can only be called while the instance is in the "inactive" state; the only exception is Subscription#setRequestedMaxFrequency.

### Parameters
#### Path Parameters
* **subscriptionMode** (String) - Required - The subscription mode for the items, required by Lightstreamer Server. Permitted values are: MERGE, DISTINCT, RAW, COMMAND.
* **items** (String | Array<String>) - Optional - An array of Strings containing a list of items to be subscribed to through the server. In case of a single-item subscription the String containing the item name can be passed in place of the array; both of the following examples represent a valid subscription: `new Subscription(mode,"item1",fieldList);` `new Subscription(mode,["item1","item2"],fieldList);` It is also possible to pass null (or nothing) and specify the "Item List" or "Item Group" later through Subscription#setItems and Subscription#setItemGroup. In this case the fields parameter must not be specified.
* **fields** (Array<String>) - Optional - An array of Strings containing a list of fields for the items to be subscribed to through Lightstreamer Server. It is also possible to pass null (or nothing) and specify the "Field List" or "Field Schema" later through Subscription#setFields and Subscription#setFieldSchema. In this case the items parameter must not be specified.
```

--------------------------------

### getNotificationFormat

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnSubscription.html

Gets the JSON structure requested by the user to be used as the format of push notifications. This JSON structure is sent by the server to the push notification service provider (FCM or APNs), hence it must follow its specifications.

```APIDOC
## getNotificationFormat()

### Description
Inquiry method that gets the JSON structure requested by the user to be used as the format of push notifications.  
This JSON structure is sent by the server to the push notification service provider (FCM or APNs), hence it must follow its specifications.  

See:
    
  * #setNotificationFormat
  * #getActualNotificationFormat

### Returns:
the JSON structure requested by the user to be used as the format of push notifications.

Type
     String
```

--------------------------------

### DynaGrid Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/DynaGrid.html

Creates a DynaGrid instance to display subscription data in a dynamically generated HTML grid. The grid rows are cloned from a specified HTML template.

```APIDOC
## new DynaGrid(id, autoParse)

### Description
Creates an object that extends AbstractGrid displaying its values in a grid made of HTML elements. The grid rows are displayed into dynamically generated HTML rows. The object can be supplied to Subscription#addListener and Subscription#removeListener in order to display data from one or more Subscriptions.

### Parameters
#### Path Parameters
- **id** (String) - Required - The HTML "id" attribute of the HTML element that represents the template from which rows of the grid will be cloned. The template can be either a visible or a hidden part of the page; anyway, it will become invisible as soon as the AbstractGrid#parseHtml method is executed.
- **autoParse** (boolean) - Required - If true the AbstractGrid#parseHtml method is executed before the constructor execution is completed. If false the parseHtml method has to be called later by custom code. It can be useful to set this flag to false if, at the time of the DynaGrid instance creation, the HTML element designated as template is not yet ready on the page.

### Extends
* AbstractGrid
```

--------------------------------

### onListenStart

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/AbstractWidget.html

Event handler that receives a notification when the SubscriptionListener instance is added to a Subscription. This is the first event fired on the listener.

```APIDOC
## onListenStart()

### Description
Event handler that receives a notification when the SubscriptionListener instance is added to a Subscription through Subscription#addListener. This is the first event to be fired on the listener.

### Overrides
* SubscriptionListener#onListenStart
```

--------------------------------

### Enable Client Logging

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/index.html

Configure the Lightstreamer client to log debug information by creating a ConsoleLoggerProvider and setting it as the default. This is useful for troubleshooting.

```javascript
var loggerProvider = new ConsoleLoggerProvider(ConsoleLogLevel.DEBUG);
LightstreamerClient.setLoggerProvider(loggerProvider);

```

--------------------------------

### StatusWidget Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/StatusWidget.html

Creates a new StatusWidget instance to listen for Lightstreamer client events and display connection status. The widget can be attached to the page border or positioned manually.

```APIDOC
## new StatusWidget(attachToBorder, distance, fromTop, initialDisplayopt)

### Description
Creates an object to be used to listen to events from a LightstreamerClient instance. The new object will create a small visual widget to display the status of the connection. The created widget will have a fixed position so that it will not move when the page is scrolled.

### Parameters
#### Path Parameters
- **attachToBorder** (String) - Required - "left" "right" or "no" to specify if the generated widget should be attached to the left border, right border or should not be attached to any border. In the latter case, it should be immediately positioned manually, by acting on the DOM element obtained through StatusWidget#getDomNode.
- **distance** (String) - Required - The distance of the widget from the top/bottom (depending on the fromTop parameter). The specified distance must also contain the units to be used: all and only the units supported by CSS are accepted.
- **fromTop** (boolean) - Required - true or false to specify if the distance is related to the top or to the bottom of the page.
- **initialDisplay** (String) - Optional - "open" "closed" or "dyna" to specify if the generated widget should be initialized open, closed or, in the "dyna" case, open and then immediately closed. By default "dyna" is used. If attachToBorder is set to "no" then this setting has no effects.

### Throws
- IllegalArgumentException: if an invalid value was passed as attachToBorder parameter.
```

--------------------------------

### MpnSubscription Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnSubscription.html

Creates an MpnSubscription object to describe an MPN subscription for Lightstreamer Server's MPN Module. This object can be used with LightstreamerClient#subscribeMpn. Methods for describing the subscription can only be called when the instance is in the 'inactive' state. Alternatively, an MpnSubscription can be initialized by copying properties from an existing Subscription or MpnSubscription object.

```APIDOC
## new MpnSubscription(subscriptionMode, items, fields)

### Description
Creates an object to be used to describe an MPN subscription that is going to be subscribed to through the MPN Module of Lightstreamer Server. The object can be supplied to LightstreamerClient#subscribeMpn in order to bring the MPN subscription to "active" state. Note that all of the methods used to describe the subscription to the server can only be called while the instance is in the "inactive" state. Alternatively you can create an MpnSubscription object by passing a single argument either of type Subscription or MpnSubscription.

### Parameters
#### Path Parameters
- **subscriptionMode** (String) - Required - The subscription mode for the items, required by Lightstreamer Server. Permitted values are: `MERGE`, `DISTINCT`.
- **items** (String | Array<String>) - Required - An array of items to be subscribed to through Lightstreamer Server. It is also possible specify the "Item List" or "Item Group" later through MpnSubscription#setItems and MpnSubscription#setItemGroup.
- **fields** (Array<String>) - Required - An array of fields for the items to be subscribed to through Lightstreamer Server. It is also possible to specify the "Field List" or "Field Schema" later through MpnSubscription#setFields and MpnSubscription#setFieldSchema.

### Throws
- IllegalArgumentException If no or invalid subscription mode is passed.
- IllegalArgumentException If either the items or the fields array is left null.
- IllegalArgumentException If the specified "Item List" or "Field List" is not valid; see MpnSubscription#setItems and MpnSubscription#setFields for details.
```

--------------------------------

### AbstractWidget Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/AbstractWidget.html

This is an abstract class and should not be instantiated directly. Use subclasses like Chart or AbstractGrid.

```APIDOC
## AbstractWidget Constructor

#### new AbstractWidget()

This is an abstract class; no instances of this class should be created.

See:
    
  * Chart
  * AbstractGrid

### Extends
  * SubscriptionListener
```

--------------------------------

### MpnDevice.addListener

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnDevice.html

Adds a listener to receive events from the MpnDevice instance. The same listener can be added to multiple MpnDevice instances.

```APIDOC
## addListener(listener)

### Description
Adds a listener that will receive events from the MpnDevice instance. The same listener can be added to several different MpnDevice instances.

**Lifecycle:** a listener can be added at any time.

### Parameters
#### Path Parameters
- **listener** (MpnDeviceListener) - Required - An object that will receive the events as shown in the MpnDeviceListener interface. Note that the given instance does not have to implement all of the methods of the MpnDeviceListener interface. In fact it may also implement none of the interface methods and still be considered a valid listener. In the latter case it will obviously receive no events.
```

--------------------------------

### addListener(listener)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/Subscription.html

Adds a listener to receive events from the Subscription instance. The same listener can be added to multiple Subscription instances. Listeners can be added at any time.

```APIDOC
## addListener(listener)

### Description
Adds a listener that will receive events from the Subscription instance. The same listener can be added to several different Subscription instances.

### Parameters
#### Parameters
- **listener** (SubscriptionListener) - An object that will receive the events as shown in the SubscriptionListener interface. Note that the given instance does not have to implement all of the methods of the SubscriptionListener interface. In fact it may also implement none of the interface methods and still be considered a valid listener. In the latter case it will obviously receive no events.
```

--------------------------------

### configureArea(chartCssopt, chartHeightopt, chartWidthopt, chartTopopt, chartLeftopt)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/Chart.html

Sets the stylesheet and positioning for the chart area. This allows customization of the chart's appearance and layout within its container.

```APIDOC
## configureArea(chartCssopt, chartHeightopt, chartWidthopt, chartTopopt, chartLeftopt)

### Description
Setter method that sets the stylesheet and positioning to be applied to the chart area.

### Lifecycle
The chart area stylesheet and position attributes can be set and changed at any time.

### Parameters
#### Path Parameters
* **chartCss** (String) - Optional - the name of an existing stylesheet to be applied to the chart. If not set, the stylesheet is inherited from the DOM element containing the chart.
* **chartHeight** (Number) - Optional - the height in pixels of the chart area. Such height may be set as smaller than the height of the container HTML element in order to make room for the X axis labels. If not set, the whole height of the container HTML element is used.
* **chartWidth** (Number) - Optional - the width in pixels of the chart area. Such width may be set as smaller than the width of the container HTML element in order to make room for the Y axis labels. If not set, the whole width of the container HTML element is used.
* **chartTop** (Number) - Optional - Default: 0 - the distance in pixels between the top margin of the chart area and the top margin of the container HTML element. Such distance may be set as a nonzero value in order to make room for the first Y axis label. If not set, 0 is used.
* **chartLeft** (Number) - Optional - Default: 0 - the distance in pixels between the left margin of the chart area and the left margin of the container HTML element. Such distance may be set as a nonzero value in order to make room for the Y axis labels. If not set, 0 is used.

### Throws
* IllegalArgumentException: if one of the numeric values is not valid.
```

--------------------------------

### getStalledTimeout()

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/ConnectionOptions.html

Retrieves the extra time the client can wait when no keepalive packet or data is received before entering the 'STALLED' status.

```APIDOC
## getStalledTimeout()

### Description
Inquiry method that gets the extra time the client can wait when an expected keepalive packet has not been received on a stream connection (and no actual data has arrived), before entering the "STALLED" status.

### Returns
The idle time (in milliseconds) admitted before entering the "STALLED" status.

### Type
Number
```

--------------------------------

### MpnSubscription.addListener

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnSubscription.html

Adds a listener to the MpnSubscription instance to receive events. The same listener can be added to multiple MpnSubscription instances. Listeners can be added at any time.

```APIDOC
## addListener(listener)

### Description
Adds a listener that will receive events from the MpnSubscription instance. The same listener can be added to several different MpnSubscription instances.

### Parameters
#### Path Parameters
- **listener** (MpnSubscriptionListener) - Required - An object that will receive the events as shown in the MpnSubscriptionListener interface. Note that the given instance does not have to implement all of the methods of the MpnSubscriptionListener interface. In fact it may also implement none of the interface methods and still be considered a valid listener. In the latter case it will obviously receive no events.
```

--------------------------------

### setAddOnTop(isAddOnTop)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/StaticGrid.html

Setter method that decides whenever new rows entering the model will be placed at the top of the grid or at the bottom. This setting can be changed at any time, but changing it while the internal model is not empty may result in an inconsistent view.

```APIDOC
## setAddOnTop(isAddOnTop)

### Description
Setter method that decides whenever new rows entering the model will be placed at the top of the grid or at the bottom. Note that if the sort is enabled on the Grid through AbstractGrid#setSort then this setting is ignored as new rows will be placed on their right position based on the sort configuration. Also note that the sort/add policy may be ignored depending on the grid configuration; see the use of the "data-item" cell attribute in StaticGrid.

### Default value
false

### Lifecycle
this setting can be changed at any time. Note anyway that changing this setting while the internal model is not empty may result in a incosistent view.

### Parameters
#### Path Parameters
* **isAddOnTop** (boolean) - Required - true/false to place new rows entering the model as the first/last row of the grid.

### Overrides
* AbstractGrid#setAddOnTop

### Throws
* IllegalArgumentException - if the given value is not a valid boolean value.
```

--------------------------------

### warn(message, exceptionopt)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/Logger.html

Logs messages at the WARN level. It accepts a message string and an optional exception object.

```APIDOC
## warn(message, exceptionopt)

### Description
Receives log messages at WARN level.

### Parameters
#### Path Parameters
- **message** (String) - Required - The message to be logged.
- **exception** (Error) - Optional - An Exception instance related to the current log message.
```

--------------------------------

### onCommandSecondLevelItemLostUpdates(lostUpdates, key)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/AbstractGrid.html

Event handler called when Lightstreamer Server drops updates for a second-level subscription item. Allows for recovery actions.

```APIDOC
## onCommandSecondLevelItemLostUpdates(lostUpdates, key)

### Description
Event handler that is called by Lightstreamer to notify that, due to internal resource limitations, Lightstreamer Server dropped one or more updates for an item that was subscribed to as a second-level subscription. Such notifications are sent only if the Subscription was configured in unfiltered mode (second-level items are always in "MERGE" mode and inherit the frequency configuration from the first-level Subscription).
By implementing this method it is possible to perform recovery actions.

### Parameters
#### Path Parameters
- **lostUpdates** (Number) - Required - The number of consecutive updates dropped for the item.
- **key** (String) - Required - The value of the key that identifies the second-level item.
```

--------------------------------

### Chart Constructor

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/Chart.html

Creates a Chart widget instance attached to a specified HTML element.

```APIDOC
## new Chart(id)

### Description
Creates an object that extends AbstractWidget displaying its values as a multiline chart. The AbstractWidget#parseHtml method is automatically called by this constructor.

### Parameters
#### Path Parameters
- **id** (String) - Required - The HTML "id" attribute of a DOM Element to which the chart will be attached.
```

--------------------------------

### setAddOnTop(isAddOnTop)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/DynaGrid.html

Setter method that decides whenever new rows entering the model will be placed at the top of the grid or at the bottom. Note that if the sort is enabled on the Grid through AbstractGrid#setSort then this setting is ignored as new rows will be placed on their right position based on the sort configuration. This setting can be changed at any time.

```APIDOC
## setAddOnTop(isAddOnTop)

### Description
Decides whether new rows entering the model will be placed at the top or bottom of the grid. This setting is ignored if sorting is enabled. Changing this setting while the internal model is not empty may result in an inconsistent view.

### Method
setAddOnTop

### Parameters
#### Path Parameters
- **isAddOnTop** (boolean) - Required - true/false to place new rows entering the model as the first/last row of the grid.

### Throws
- **IllegalArgumentException**: if the given value is not a valid boolean value.
```

--------------------------------

### setAddOnTop(isAddOnTop)

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/AbstractGrid.html

Decides whenever new rows entering the model will be placed at the top of the grid or at the bottom. This setting is ignored if sorting is enabled.

```APIDOC
## setAddOnTop(isAddOnTop)

### Description
Setter method that decides whenever new rows entering the model will be placed at the top of the grid or at the bottom.

### Parameters
#### Path Parameters
* **isAddOnTop** (boolean) - Required - true/false to place new rows entering the model as the first/last row of the grid.

### Default Value
false

### Lifecycle
This setting can be changed at any time. Note anyway that changing this setting while the internal model is not empty may result in a inconsistent view.

### Throws
* IllegalArgumentException - if the given value is not a valid boolean value.

### Notes
* If the sort is enabled on the Grid through AbstractGrid#setSort then this setting is ignored as new rows will be placed on their right position based on the sort configuration.
* The sort/add policy may be ignored depending on the grid configuration; see the use of the "data-item" cell attribute in StaticGrid.
```

--------------------------------

### MpnDevice.getListeners

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/MpnDevice.html

Returns an array of all MpnDeviceListener instances that have been added to this client.

```APIDOC
## getListeners()

### Description
Returns an array containing the MpnDeviceListener instances that were added to this client.

### Returns
an Array containing the listeners that were added to this client. Listeners added multiple times are included multiple times in the array.

Type
     Array.<MpnDeviceListener>
```

--------------------------------

### StatusWidget Parameters

Source: https://lightstreamer.com/sdks/ls-web-client/9.0.0/api/StatusWidget.html

The StatusWidget accepts a 'chngStatus' parameter to update the client's connection status. This parameter is a string that can take several predefined values, each indicating a specific state of the Lightstreamer client's connection.

```APIDOC
## Parameters

### `chngStatus` (String) - Required

The new status of the client. Possible values include:
- "CONNECTING": Client is attempting to establish a connection.
- "CONNECTED:STREAM-SENSING": Client is evaluating the streaming connection.
- "CONNECTED:WS-STREAMING": Streaming connection over WebSocket established.
- "CONNECTED:HTTP-STREAMING": Streaming connection over HTTP established.
- "CONNECTED:WS-POLLING": Polling connection over WebSocket started.
- "CONNECTED:HTTP-POLLING": Polling connection over HTTP started.
- "STALLED": Streaming session has been silent.
- "DISCONNECTED:WILL-RETRY": Connection closed, a new attempt will be made.
- "DISCONNECTED:TRYING-RECOVERY": Connection closed, attempting recovery.
- "DISCONNECTED": Connection closed, no automatic reconnection.
```
Tokens:
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