变量的LIfetime

Question

我在理解下面的全局变量x的生命周期时遇到了一些困难。我对我的问题作了评论，我不理解。请帮帮我..。谢斯

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

下面是所有Javascript引擎如何通过变量提升来处理代码(实际上)

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/>";
}

希望这能有所帮助

函数中的var x意味着全局x是无关的(当然，可以在浏览器中使用window.x访问，在其他环境中使用其他“全局”对象)。