Deferred JS loading
Deferred JS loading is a technique for loading JavaScript files in a non-blocking way using the defer attribute on a <script> tag. A deferred script is downloaded in parallel while the browser parses the HTML, but it is only executed after the HTML document has been fully parsed. This method is critical for preventing JavaScript from being a render-blocking resource, which improves the First Contentful Paint (FCP) by ensuring scripts do not delay the initial rendering of the page.
Related web performance terms
- DOM (Document Object Model)
The DOM is a tree-like representation of all the elements in an HTML document that is created by the browser when it loads a page.
- DOM Content Loaded
DOM Content Loaded (DOMContentLoaded or DCL) is a browser event that fires when the initial HTML document has been completely loaded and parsed, without waiting for stylesheets, images, and subframes to finish loading.
- DOM Size
DOM Size refers to the total number of elements (nodes) and the complexity of their nesting within a page's HTML structure.
- Deployment
A deployment is the process of releasing new code, features, or content updates to a live production website. This is a critical event for any caching system, as the cached content may become instantly outdated.