### Initializing Google Analytics Tracking (JavaScript)

Source: https://github.com/explv/explv.github.io/blob/master/index.html

This snippet initializes Google Analytics tracking by setting up the `dataLayer` array and defining the `gtag` function. It then configures the analytics for the specified tracking ID 'UA-111933116-1', enabling data collection for page views and other events.

```JavaScript
window.dataLayer = window.dataLayer || [];
function gtag() { dataLayer.push(arguments); }
gtag('js', new Date());
gtag('config', 'UA-111933116-1');
```

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

### Conditionally Loading External JavaScript Libraries

Source: https://github.com/explv/explv.github.io/blob/master/index.html

This code block checks for the existence of global objects (jQuery, jQuery UI, Bootstrap's modal function, and Leaflet's `L` object) and, if they are not found, dynamically writes a `<script>` tag to the document to load the respective external JavaScript library. This ensures that libraries are only loaded if they haven't been loaded already, preventing redundant requests and optimizing page load.

```JavaScript
window.jQuery || document.write('<script type="text/javascript" src="js/external/jquery-3.2.1.min.js"></script>');
window.jQuery.ui || document.write('<script type="text/javascript" src="js/external/jquery-ui.min.js"></script>');
window.jQuery.fn.modal || document.write('<script type="text/javascript" src="js/external/bootstrap.min.js"></script>');
window.L || document.write('<script type="text/javascript" src="js/external/leaflet.js"></script>');
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.