Extension content primarily refers to the components provided by browser extensions that interact directly with the content and structure of web pages you visit. The most prominent example of this is content scripts.
Content scripts are extension-provided scripts which run in the context of a web page. This means they operate within the same environment as the page's own scripts, allowing them to read details of the web pages the browser visits, make changes to them, and pass information to their parent extension.
How Content Scripts Work
Content scripts act as a bridge between an extension and a web page. They allow extensions to modify the behavior and appearance of specific web pages, injecting additional features or information.
- Accessing the DOM: Content scripts can access and manipulate the Document Object Model (DOM) of the page. This means they can read page elements, change styles, add new elements, or remove existing ones.
- Interacting with JavaScript: They can interact with the JavaScript running on the page, although they operate in an isolated world by default to prevent conflicts.
- Communication: Content scripts can communicate with the background script or other parts of the extension to exchange messages and data.
Content Scripts vs. Page Scripts
It's important to distinguish content scripts from the scripts loaded by the web page itself (those included in <script> elements within the page's HTML).
| Feature | Content Scripts | Page Scripts |
|---|---|---|
| Source | Provided by a browser extension | Loaded by the web page itself |
| Execution | Run in the context of a web page | Run within the page's own environment |
| Purpose | Enhance/modify page behavior for user | Define core page functionality/content |
| Access | Access to the page's DOM and scripts | Access to the page's DOM and other scripts |
| Relationship | Can interact with the page | Form part of the page's structure |
As highlighted in the reference, this differs from scripts which are loaded by the page itself, including those which are provided in <script elements within the page. Content scripts are specifically extension-provided code running alongside, but separate from, the page's own code.
In essence, when you install an extension that alters how a website looks or behaves (like an ad blocker, a dark mode toggle, or a grammar checker), it's likely using extension content in the form of content scripts to achieve this on the visited page.
