chrome extension官方reference摘要

At a high level, we'll use it to declare to Chrome what the extension is going to do, and what permissions it requires in order to do those things.

Many extensions have a background page, an invisible page that holds the main logic of the extension. An extension can also contain other pages that present the extension's UI. If an extension needs to interact with web pages that the user loads (as opposed to pages that are included in the extension), then the extension must use a content script.

There are two types of background pages: persistent background pages, and event pages. Persistent background pages, as the name suggests, are always open. Event pages are opened and closed as needed. Unless you absolutely need your background page to run all the time, prefer to use an event page.

The HTML pages inside an extension have complete access to each other's DOMs, and they can invoke functions on each other.

If your extension needs to interact with web pages, then it needs a content script. A content script is some JavaScript that executes in the context of a page that's been loaded into the browser. Think of a content script as part of that loaded page, not as part of the extension it was packaged with (its parent extension).

Content scripts can read details of the web pages the browser visits, and they can make changes to the pages.

In the following figure, the content script can read and modify the DOM for the displayed web page. It cannot, however, modify the DOM of its parent extension's background page.

Content scripts aren't completely cut off from their parent extensions. A content script can exchange messages with its parent extension, as the arrows in the following figure show. For example, a content script might send a message whenever it finds an RSS feed in a browser page. Or a background page might send a message asking a content script to change the appearance of its browser page.

In addition to having access to all the APIs that web pages and apps can use, extensions can also use Chrome-only APIs (often called chrome.* APIs) that allow tight integration with the browser. For example, any extension or web app can use the standard window.open() method to open a URL. But if you want to specify which window that URL should be displayed in, your extension can use the Chrome-only tabs.create method instead.

The HTML pages within an extension often need to communicate. Because all of an extension's pages execute in same process on the same thread, the pages can make direct function calls to each other.