Question

我正在使用HTML / Javascript编写Google Chrome扩展程序。我试图使用一个全局变量在两个函数之间传递信息，但是即使我在一个函数中分配我的变量，当我从另一个函数中读取它时它也没有改变。

    var type = 0; //define global variable
    window.onload=function(){onCreated()}; //set onCreated function to run after loading HTML

    function onCreated()
    {
        chrome.history.search({'text': ''},function(historyItems){gotHistory(historyItems)});//search for historyItems and then pass them to the gotHistory function
    }

    function gotHistory(historyItems)
    {
        var idcount=0;//used to increment the ids of each new element added
        for(var count=0; count < historyItems.length; count++)//go through each history item
        {
            chrome.history.getVisits({'url':historyItems[count].url}, function(visitItems){gotVisits(visitItems)}); //search for visitItems for the url and pass the results to gotVisists function (atm all this function does is assign the global variable to =3)

            var body = document.getElementById("outputid");//find the body of the HTML
            var newt = document.createElement("p");//create a new element
            newt.setAttribute("id","url"+idcount);//give it a unique id

            newt.innerHTML = historyItems[count].title;//set the text to say the title of the url

            if(type != 0)//if the other function was successful, type=3 and the text should be green
            {
                newt.style.color="green";
            }   

            body.appendChild(newt);//add the new element to the body
            idcount++;

        }
    }
    function gotVisits(visitItems)
    {
//assign the global variable to be 3
        type = 3;
    }

但是，元素永远不是绿色。他们应该永远是绿色的。这意味着在函数gotVisits中，类型未成功分配给3。谁能解释一下这里发生了什么？

干杯，

马特 p.s我意识到这里的gotVisits功能真的没用，但是我用它来证明一点。实际上，我将使用它将有用的信息传递给

Answer 1

而不是：

var type = 0;

尝试：

window.type = 0;

您也可以选择使用闭包，例如：

(function() {

var type = 0;

    var type = 0; //define global variable
    window.onload=function(){onCreated()}; //set onCreated function to run after loading HTML

    function onCreated()
    {
        chrome.history.search({'text': ''},function(historyItems){gotHistory(historyItems)});//search for historyItems and then pass them to the gotHistory function
    }

    function gotHistory(historyItems)
    {
        var idcount=0;//used to increment the ids of each new element added
        for(var count=0; count < historyItems.length; count++)//go through each history item
        {
            chrome.history.getVisits({'url':historyItems[count].url}, function(visitItems){gotVisits(visitItems)}); //search for visitItems for the url and pass the results to gotVisists function (atm all this function does is assign the global variable to =3)

            var body = document.getElementById("outputid");//find the body of the HTML
            var newt = document.createElement("p");//create a new element
            newt.setAttribute("id","url"+idcount);//give it a unique id

            newt.innerHTML = historyItems[count].title;//set the text to say the title of the url

            if(type != 0)//if the other function was successful, type=3 and the text should be green
            {
                newt.style.color="green";
            }   

            body.appendChild(newt);//add the new element to the body
            idcount++;

        }
    }
    function gotVisits(visitItems)
    {
//assign the global variable to be 3
        type = 3;
    }

})();

这样可以避免污染window对象，无论如何都应该避免这种情况，并允许内部函数访问type变量。

它应该做你想要的。

window.onload的外部函数包装器也是多余的，只需执行：

window.onload = onCreated;

Answer 2

看起来chrome.history.getVisits异步执行回调，因此您首先尝试检查该变量，并在以后更新。您可以使用一对console.log消息对此进行验证。

将其余代码移动到回调中，以便在正确的时间执行。

全局变量不在功能之间分配

2 个答案: