同步执行异步功能 [英] Executing asynchronous function , synchronously

问题描述

我正在制作Chrome扩展程序，通过弹出窗口阻止添加到本地存储的特定网站。我认为这个代码中的问题是，它在chrome.storage.local.get的回调完成之前返回。

I am making a chrome extension that blocks specific sites added to local storage through popup window. I think the problem in this code is, it returns before completion of chrome.storage.local.get's callback. How can I make it wait for sometime before returning ?

chrome.webRequest.onBeforeRequest.addListener(
function(details) {

var matched = false;

chrome.storage.local.get ( 'blocked_sites', function ( sites ) {
   var bsites = sites.blocked_sites;
   for ( i = 0, size = bsites.length; i < size; i++ ) {
    if ( details.url.indexOf( "://" + bsites[i] + "/" ) != -1 ) {
      matched = true;
    } // end if 
  } // end for

});
// WAIT HERE FOR VALUE OF MATCHED TO BE SET BY CALLBACK
return { cancel: matched };
},
{ urls: ["<all_urls>"] },
["blocking"] );

chrome.storage.local.set({'blocked_sites': [ 'www.topnotchdev.com'] }, null);

推荐答案

em>异步函数 webRequest 阻止侦听器。这是没有办法的，哈克或其他。由于JavaScript是单线程的，因此基本上是不可能的;在当前函数执行完成之前，异步操作甚至不会启动。

You can't call any asynchronous function in webRequest blocking listeners. There is no way around it, hacky or otherwise. It is fundamentally impossible, since JavaScript is single-threaded; an async operation won't even start before the current function finishes executing.

这意味着您不能依赖异步存储;您必须拥有本地同步缓存。

This means you cannot rely on asynchronous storage; you must have a local synchronous cache for it.

将 blocked_sites 保存到一个变量中，并在 chrome.storage.onChanged 事件。这样，您将拥有设置的同步缓存。

Save blocked_sites to a variable, and update it on chrome.storage.onChanged event. This way, you'll have a synchronous cache of the setting.

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