Chrome扩展程序，javascript：这是为什么发射两次？ [英] Chrome extension, javascript: Why is this firing twice?

问题描述

  function test（）$ b在我的（测试）Chrome扩展中有一个非常简单的代码： $ b {
 alert（In test！）; 
 
 
 chrome.tabs.onUpdated.addListener（函数（tabid，changeinfo，tab）{
 var url = tab.url; 
 if（url！= =未定义）{
 
 test（）; 
} 
}）; 
  

我的问题是，为什么 test（）发射两次？而且更重要的是，我该如何让它燃烧一次？ 看看事件发生时不同的状态被派遣。我认为，当国家加载或国家完成时，它会被派遣一次。如果是这样的话，那么你的问题将被解决：

  function test（）
 {
警报（测试中！）; 
 
 
 chrome.tabs.onUpdated.addListener（函数（tabid，changeinfo，tab）{
 var url = tab.url; 
 if（url！= = undefined&&; changeinfo.status ==complete）{
 
 test（）; 
} 
}）; 
  

I have a very very simple bit of code in my (test) Chrome extension:

    function test()
    {
    alert("In test!");
    }

   chrome.tabs.onUpdated.addListener(function(tabid, changeinfo, tab) {
    var url = tab.url;
        if (url !== undefined) {

        test();
    }
   });

My question is, why is test() firing twice? And more importantly, how do I make it fire just once?

解决方案

Have a look at what the different states are when the event is dispatched. I presume, that it is getting dispatched once when the state is "loading" or when the state is "complete". If that is the case, then your problem would be fixed with:

 function test()
    {
    alert("In test!");
    }

   chrome.tabs.onUpdated.addListener(function(tabid, changeinfo, tab) {
    var url = tab.url;
        if (url !== undefined && changeinfo.status == "complete") {

        test();
    }
   });

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