问题描述

我有一个要使用chrome.tabs.executeScript在页面中执行的函数，该函数从浏览器操作弹出窗口运行。权限设置正确，并与同步回调配合使用：

chrome.tabs.executeScript(
    tab.id, 
    { code: `(function() { 
        // Do lots of things
        return true; 
    })()` },
    r => console.log(r[0])); // Logs true

问题是我要调用的函数经历了几次回调，所以我想使用async和await：

chrome.tabs.executeScript(
    tab.id, 
    { code: `(async function() { 
        // Do lots of things with await
        return true; 
    })()` },
    async r => {
        console.log(r); // Logs array with single value [Object]
        console.log(await r[0]); // Logs empty Object {}
    }); 

问题是回调结果r。它应该是一个脚本结果数组，所以我希望r[0]是在脚本完成时解析的承诺。

Promise语法(使用.then())也不起作用。

如果我在页面中执行完全相同的函数，它将按预期返回承诺，并且可以等待。

你知道我做错了什么吗？有什么办法可以绕过它吗？

推荐答案

问题是在页面和扩展之间不能直接使用事件和本机对象。从本质上讲，您会得到一个序列化副本，如果您这样做了JSON.parse(JSON.stringify(obj))，就会得到类似的东西。

这意味着某些本机对象(例如new Error或new Promise)将被清空(变为{})，事件丢失，Promise的实现无法跨边界工作。

解决方案是在脚本中使用chrome.runtime.sendMessage返回消息，在popup.js中使用chrome.runtime.onMessage.addListener进行监听：

chrome.tabs.executeScript(
    tab.id, 
    { code: `(async function() { 
        // Do lots of things with await
        let result = true;
        chrome.runtime.sendMessage(result, function (response) {
            console.log(response); // Logs 'true'
        });
    })()` }, 
    async emptyPromise => {

        // Create a promise that resolves when chrome.runtime.onMessage fires
        const message = new Promise(resolve => {
            const listener = request => {
                chrome.runtime.onMessage.removeListener(listener);
                resolve(request);
            };
            chrome.runtime.onMessage.addListener(listener);
        });

        const result = await message;
        console.log(result); // Logs true
    }); 

我已经extended this into a function chrome.tabs.executeAsyncFunction(作为chrome-extension-async的一部分，它‘代理’整个API)：

function setupDetails(action, id) {
    // Wrap the async function in an await and a runtime.sendMessage with the result
    // This should always call runtime.sendMessage, even if an error is thrown
    const wrapAsyncSendMessage = action =>
        `(async function () {
    const result = { asyncFuncID: '${id}' };
    try {
        result.content = await (${action})();
    }
    catch(x) {
        // Make an explicit copy of the Error properties
        result.error = { 
            message: x.message, 
            arguments: x.arguments, 
            type: x.type, 
            name: x.name, 
            stack: x.stack 
        };
    }
    finally {
        // Always call sendMessage, as without it this might loop forever
        chrome.runtime.sendMessage(result);
    }
})()`;

    // Apply this wrapper to the code passed
    let execArgs = {};
    if (typeof action === 'function' || typeof action === 'string')
        // Passed a function or string, wrap it directly
        execArgs.code = wrapAsyncSendMessage(action);
    else if (action.code) {
        // Passed details object https://developer.chrome.com/extensions/tabs#method-executeScript
        execArgs = action;
        execArgs.code = wrapAsyncSendMessage(action.code);
    }
    else if (action.file)
        throw new Error(`Cannot execute ${action.file}. File based execute scripts are not supported.`);
    else
        throw new Error(`Cannot execute ${JSON.stringify(action)}, it must be a function, string, or have a code property.`);

    return execArgs;
}

function promisifyRuntimeMessage(id) {
    // We don't have a reject because the finally in the script wrapper should ensure this always gets called.
    return new Promise(resolve => {
        const listener = request => {
            // Check that the message sent is intended for this listener
            if (request && request.asyncFuncID === id) {

                // Remove this listener
                chrome.runtime.onMessage.removeListener(listener);
                resolve(request);
            }

            // Return false as we don't want to keep this channel open https://developer.chrome.com/extensions/runtime#event-onMessage
            return false;
        };

        chrome.runtime.onMessage.addListener(listener);
    });
}

chrome.tabs.executeAsyncFunction = async function (tab, action) {

    // Generate a random 4-char key to avoid clashes if called multiple times
    const id = Math.floor((1 + Math.random()) * 0x10000).toString(16).substring(1);

    const details = setupDetails(action, id);
    const message = promisifyRuntimeMessage(id);

    // This will return a serialised promise, which will be broken
    await chrome.tabs.executeScript(tab, details);

    // Wait until we have the result message
    const { content, error } = await message;

    if (error)
        throw new Error(`Error thrown in execution script: ${error.message}.
Stack: ${error.stack}`)

    return content;
}

这个executeAsyncFunction可以这样调用：

const result = await chrome.tabs.executeAsyncFunction(
    tab.id, 
    // Async function to execute in the page
    async function() { 
        // Do lots of things with await
        return true; 
    });

This包装chrome.tabs.executeScript和chrome.runtime.onMessage.addListener，并将脚本包装在try-finally中，然后调用chrome.runtime.sendMessage解析承诺。

这篇关于使用chrome.tab.ecuteScript执行异步函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！