初学闭包，不太明白，求大神指教

Question

function box() {

    var arr = [];

    for (var i = 0; i < 5; i++) {

        arr[i] = function () {

            return i;

        }

    }

    return arr;

}

var b = box();

for (var i = 0; i < 5; i++) {

    alert(b[i]);

}     

当box()执行完之后，为什么arr[0]到arr[4]里面的值都是function () { return i;}
为什么不依次是：function () {return 0;}，function () {return 1;}。。。

Answer 1

因为闭包只能取得包含函数中任何变量的最后一个值，在这里指的就是i这个变量，box()函数执行后返回的是一个函数数组，数组中的每一个i引用的都是同一个变量i，注意box()返回的是一个函数！所以里面的{return i}这只是函数内的一个声明，还没有执行呀，所以当然保持{return i}不变。因为引用的是同一个外部i，所以当box()函数返回后，外部变量i的值是5，此时每一个return中都引用着保存变量i的同一个变量对象，所以如果最后执行了内部的arr[]中的函数，最后每个函数内部的i的值都是5.//执行内部返回的arr中的函数，当然box()[1]()、box()[2]()、box()[3]()...都返回5；&nbsp; &nbsp; function box() {&nbsp; &nbsp; &nbsp; &nbsp; var arr = [];&nbsp; &nbsp; &nbsp; &nbsp; for (var i = 0; i < 5; i++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;arr[i] = function () {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return i;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return arr;&nbsp; &nbsp; }&nbsp;&nbsp; &nbsp; box()[1](); //执行后返回5//不执行内部函数，仅仅是box()的话，当然只返回一个function咯&nbsp; &nbsp; function box() {&nbsp; &nbsp; &nbsp; &nbsp; var arr = [];&nbsp; &nbsp; &nbsp; &nbsp; for (var i = 0; i < 5; i++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;arr[i] = function () {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return i;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return arr;&nbsp; &nbsp; }&nbsp;&nbsp; &nbsp; box(); //[function, function, function, function, function]