LIfetime變量

Question

我在理解下面全局變量x的生存期時遇到了一些麻煩。我有我的評論對我不理解的問題，行..請幫助... thanksss

var target = document.getElementById("outputArea"); 
var outString = ""; 

var x = 0; 
var y = 0; 

callMeOften2(); 
callMeOften2(); 
callMeOften2(); 
outString += "<br/>"; 

target.innerHTML = outString; 

function callMeOften2() { 
    outString += x + "<br/>"; //why isn't this going to give an output of 0? but gave an output of undefined instead? isn't x referring to the global variable x? 
    var x = 100; 

    x = x + 100; 
    outString += "from callMeoften2: " + "x = " + x + "<br/>"; 
} 

Answer 1

這裏是所有的JavaScript引擎通過可變吊裝如何與你的代碼（有效）

function callMeOften2() { 
    var x = undefined; 
    outString += x + "<br/>"; //why isn't this going to give an output of 0? but gave an output of undefined instead? isn't x referring to the global variable x? 
    x = 100; 

    x = x + 100; 
    outString += "from callMeoften2: " + "x = " + x + "<br/>"; 
} 

扮演

希望這有助於

函數中的var x意味着全球x是無關緊要的（當然，可以在瀏覽器中使用window.x訪問，ロ在其他環境中其他一些「全局」對象）