# Optimize JavaScript

To ensure efficient delivery to the client, optimize the JavaScript in Visualforce pages Optimized JavaScript also improves caching and reduces load times.

To improve the JavaScript in a Visualforce page:

- Externalize JavaScript files. This process increases the number of initial HTTP requests, but it also reduces the size of individual pages and takes advantage of browser caching.

- Build custom versions of JavaScript libraries with only the functions that you need. This process significantly reduces the size of a JavaScript file. Many open-source JavaScript libraries, such as jQuery, provide this option.

- Reduce HTTP requests by combining all JavaScript files into a single file. Remove duplicate functions that can result in more than one HTTP request.

- Remove comments and whitespace. Compress the resulting file for faster downloads.

- Use static resources to serve JavaScript files. JavaScript served this way benefits from the caching and the content distribution network (CDN) built into Salesforce.

- Put scripts at the bottom of the page. If the scripts load directly before the closing `</body>` tag, the page can download other components first and render the page progressively.

  :::note
  Only move JavaScript to the bottom of the page if you’re certain that it doesn’t have any adverse effects. For example, don’t move JavaScript code snippets that require `document.write` or event handlers from the `<head>` element.
  :::

- Instead of using the `<apex:includeScript>` tag, consider using a standard HTML `<script>` tag directly before your closing `</apex:page>` tag. The `<apex:includeScript>` tag places JavaScript right before the closing `</head>` element, which causes the browser to attempt to load the JavaScript before rendering any other content on the page.

**See Also**

- [Using Static Resources](/docs/platform/salesforce-pages-developers-guide/guide/pages-resources.md)