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| -rw-r--r-- | ext/js/background/offscreen-proxy.js | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/ext/js/background/offscreen-proxy.js b/ext/js/background/offscreen-proxy.js index 2351cb96..085048c1 100644 --- a/ext/js/background/offscreen-proxy.js +++ b/ext/js/background/offscreen-proxy.js @@ -20,6 +20,32 @@ import {ExtensionError} from '../core/extension-error.js'; import {isObject} from '../core/utilities.js'; import {base64ToArrayBuffer} from '../data/sandbox/array-buffer-util.js'; +/** + * This class is responsible for creating and communicating with an offscreen document. + * This offscreen document is used to solve two issues: + * + * - Provide clipboard access for the `ClipboardReader` class in the context of a MV3 extension. + * The background service workers doesn't have access a webpage to read the clipboard from, + * so it must be done in the offscreen page. + * + * - Provide a longer lifetime for the dictionary database. The background service worker can be + * terminated by the web browser, which means that when it restarts, it has to go through its + * initialization process again. This initialization process can take a non-trivial amount of + * time, which is primarily caused by the startup of the IndexedDB database, especially when a + * large amount of dictionary data is installed. + * + * The offscreen document stays alive longer, potentially forever, which may be an artifact of + * the clipboard access it requests in the `reasons` parameter. Therefore, this initialization + * process should only take place once, or at the very least, less frequently than the service + * worker. + * + * The long lifetime of the offscreen document is not guaranteed by the spec, which could + * result in this code functioning poorly in the future if a web browser vendor changes the + * APIs or the implementation substantially, and this is even referenced on the Chrome + * developer website. + * @see https://developer.chrome.com/blog/Offscreen-Documents-in-Manifest-v3 + * @see https://developer.chrome.com/docs/extensions/reference/api/offscreen + */ export class OffscreenProxy { /** * @param {import('../extension/web-extension.js').WebExtension} webExtension |