offscreen.js

/*
Copyright (c) 2024 George Chakhidze

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

'use strict';

// Registering this listener when the script is first executed ensures that the
// offscreen document will be able to receive messages when the promise returned
// by `offscreen.createDocument()` resolves.
chrome.runtime.onMessage.addListener(handleMessages);

// This function performs basic filtering and error checking on messages before
// dispatching the
// message to a more specific message handler.
async function handleMessages(message) {
    // Return early if this message isn't meant for the offscreen document.
    if (message.target !== 'offscreen-doc') {
        return;
    }

    // Dispatch the message to an appropriate handler.
    switch (message.type) {
        case 'copy-data-to-clipboard':
            handleClipboardWrite(message.data);
            break;
        default:
            console.warn(`Unexpected message type received: '${message.type}'.`);
    }
}

// We use a <textarea> element for two main reasons:
//  1. preserve the formatting of multiline text,
//  2. select the node's content using this element's `.select()` method.
const textEl = document.querySelector('#text');

// Use the offscreen document's `document` interface to write a new value to the
// system clipboard.
//
// At the time this demo was created (Jan 2023) the `navigator.clipboard` API
// requires that the window is focused, but offscreen documents cannot be
// focused. As such, we have to fall back to `document.execCommand()`.
async function handleClipboardWrite(data) {
    try {
        // Error if we received the wrong kind of data.
        if (typeof data !== 'string') {
            throw new TypeError(
                `Value provided must be a 'string', got '${typeof data}'.`
            );
        }

        // `document.execCommand('copy')` works against the user's selection in a web
        // page. As such, we must insert the string we want to copy to the web page
        // and to select that content in the page before calling `execCommand()`.
        textEl.value = data;
        textEl.select();
        document.execCommand('copy');
    } finally {
        // Job's done! Close the offscreen document.
        window.close();
    }
}