### Zero Svelte Mutation Example

Source: https://github.com/stolinski/zero-svelte/blob/main/README.md

Illustrates how to perform a mutation (update operation) on the 'todo' data using Zero Svelte's client. This is a direct JavaScript example of interacting with the data layer.

```javascript
z.current.mutate.todo.update({ id, completed });
```

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

### Initialize Zero Svelte Options

Source: https://github.com/stolinski/zero-svelte/blob/main/README.md

Sets up the necessary options for the Zero Svelte client, including server address and schema definition. It imports environment variables for the server and the local schema.

```ts
import { PUBLIC_SERVER } from '$env/static/public';
import { Z } from 'zero-svelte';
import { schema, type Schema } from '../zero-schema.js';
// Schema is imported from wherever your Schema type lives.
// via export type Schema = typeof schema;

export function get_z_options() {
	return {
		userID: 'anon',
		server: PUBLIC_SERVER,
		schema
		// ... other options
	} as const;
}

export const z = new Z<Schema>(get_z_options());
```

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

### Basic Todo List with Zero Svelte

Source: https://github.com/stolinski/zero-svelte/blob/main/README.md

Demonstrates a basic Svelte component for managing a todo list using Zero Svelte. It includes adding new todos, displaying them, and toggling completion status.

```svelte
<script lang="ts">
	import { Query } from 'zero-svelte';
	import { z } from '$lib/z.svelte';

	// Basic: always enabled; materializes immediately
	const todos = new Query(z.current.query.todo);

	const randID = () => Math.random().toString(36).slice(2);

	function onsubmit(event: Event) {
		event.preventDefault();
		const formData = new FormData(event.target as HTMLFormElement);
		const newTodo = formData.get('newTodo') as string;
		const id = randID();
		if (newTodo) {
			z.current.mutate.todo.insert({ id, title: newTodo, completed: false });
			(event.target as HTMLFormElement).reset();
		}
	}

	function toggleTodo(event: Event) {
		const checkbox = event.target as HTMLInputElement;
		const id = checkbox.value;
		const completed = checkbox.checked;
		z.current.mutate.todo.update({ id, completed });
	}
</script>

<div>
	<h1>Todo</h1>
	<form {onsubmit}>
		<input type="text" id="newTodo" name="newTodo" />
		<button type="submit">Add</button>
	</form>
	<ul>
		{#each todos.current as todo}
			<li>
				<input
					type="checkbox"
					value={todo.id}
					checked={todo.completed}
					oninput={toggleTodo}
				/>{todo.title}
			</li>
		{/each}
	</ul>
</div>
```

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

### Throwing Enhanced Error Messages (JavaScript)

Source: https://github.com/stolinski/zero-svelte/blob/main/TODO.md

This JavaScript snippet demonstrates how to improve error reporting by including the query hash and user ID in error messages when duplicate views are detected. This provides more context for debugging.

```javascript
throw new Error(`View already exists for hash=${hash} user=${id}`);
```

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

### Context Symbol and SSR Guard (TypeScript)

Source: https://github.com/stolinski/zero-svelte/blob/main/TODO.md

This snippet shows the creation of a context symbol for inter-component communication in Svelte and its usage with setContext. It also includes a comment indicating where an optional SSR guard can be placed.

```typescript
export const ZContextKey = Symbol('z');
setContext(ZContextKey, this);
// getContext(ZContextKey)
```

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

### Svelte Effect for Query Re-subscription (Svelte)

Source: https://github.com/stolinski/zero-svelte/blob/main/TODO.md

This code snippet shows how to ensure reactive effects in Svelte correctly track the view when the query changes. By referencing '#view.current' within the effect, Svelte detects the dependency and re-subscribes appropriately.

```svelte
$effect(() => {
	const view = this.#view; // dependency
	if (view) {
		const [data, details] = view.current;
		this.current = data;
		this.details = details;
	}
});
```

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

### Update Data and Status in Zero (TypeScript)

Source: https://github.com/stolinski/zero-svelte/blob/main/TODO.md

This TypeScript snippet illustrates how to update the internal data and status of a Zero component. It bypasses internal imports and avoids unnecessary cloning by directly assigning frozen snapshots.

```typescript
#onData = (snap: HumanReadable<TReturn> | undefined, resultType: ResultType) => {
	self.#data = { '': snap as HumanReadable<TReturn> };
	self.#status = { type: resultType };
};
```

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

### Guard Materialization in ViewWrapper (TypeScript)

Source: https://github.com/stolinski/zero-svelte/blob/main/TODO.md

This snippet demonstrates how to add an 'enabled' flag to ViewWrapper to prevent materialization, network requests, and listeners when disabled. It guards the '#materializeIfNeeded()' method to be a no-op when the flag is false.

```typescript
class ViewWrapper<...> {
  constructor(..., private enabled: boolean) {}
  #materializeIfNeeded() {
    if (!this.enabled) return; // don’t materialize
    if (!this.#view) { this.#view = this.z.current.materialize(this.query); ... }
  }
}
```

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

### Gated Todo List with Zero Svelte

Source: https://github.com/stolinski/zero-svelte/blob/main/README.md

An enhanced Svelte component for managing a todo list with Zero Svelte, featuring conditional data fetching. The `todosEnabled` state controls whether the todo query materializes.

```svelte
<script lang="ts">
	import { Query } from 'zero-svelte';
	import { z } from '$lib/z.svelte';

	// Gate materialization using the `enabled` flag.
	// When false, the query won't materialize or register listeners,
	// and `current` will be the default snapshot until re-enabled.
	let todosEnabled = $state(true);
	const todos = $derived.by(() => new Query(z.current.query.todo, todosEnabled));

	const randID = () => Math.random().toString(36).slice(2);
	function onsubmit(event: Event) {
		event.preventDefault();
		const formData = new FormData(event.target as HTMLFormElement);
		const newTodo = formData.get('newTodo') as string;
		const id = randID();
		if (newTodo) {
			z.current.mutate.todo.insert({ id, title: newTodo, completed: false });
			(event.target as HTMLFormElement).reset();
		}
	}
	function toggleTodo(event: Event) {
		const checkbox = event.target as HTMLInputElement;
		const id = checkbox.value;
		const completed = checkbox.checked;
		z.current.mutate.todo.update({ id, completed });
	}
</script>

<div>
	<label>
		<input type="checkbox" bind:checked={todosEnabled} /> Enable todos query
	</label>
	<h1>Todo</h1>
	<form {onsubmit}>
		<input type="text" id="newTodo" name="newTodo" />
		<button type="submit">Add</button>
	</form>
	<ul>
		{#each todos.current as todo}
			<li>
				<input
					type="checkbox"
					value={todo.id}
					checked={todo.completed}
					oninput={toggleTodo}
				/>{todo.title}
			</li>
		{/each}
	</ul>
</div>
```

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

### Disable Server-Side Rendering (SSR)

Source: https://github.com/stolinski/zero-svelte/blob/main/README.md

A simple configuration for SvelteKit to disable server-side rendering for a specific route, likely to ensure client-side hydration works correctly with Zero.

```ts
export const ssr = false;
```

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