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.

    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.

    Note

  • 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.