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我正在将延迟的 getJSON 调用添加到 for 循环内的数组中，该循环在其成功函数中引用局部变量。我遇到的问题是，当调用成功函数时，局部变量正在从循环的最后一次迭代中获取值。请参见下面的示例：

var calls = [];
var arr = ['a','b','c'];
for (var a in arr) {
    calls.push(
        $.getJSON(window.location, function() { alert(arr[a]); })
    );
}
$.when.apply($,calls);

jsFiddle：http: //jsfiddle.net/Me5rV/

这会产生三个值为“c”的警报，而我想要值“a”、“b”和“c”。这可能吗？

编辑：下面的作品，但我不完全确定为什么会有所不同？

var calls = [];
var arr = ['a','b','c'];
for (var a in arr) {
    calls.push(
        $.getJSON(window.location, function(x) {
            alert(x);
       }(arr[a]))
    );
}
$.when.apply($,calls);

jsFiddle：http: //jsfiddle.net/Me5rV/1/

4

1 回答 1

1

回顾一下这样的循环：

var a = [];

for( var i = 0; i < 3; ++i ) {
    a.push( function() {
        alert(i);
    });
}

实际上是：

var a = [], i = 0;

a.push( function(){
    alert(i);
});

i++;

a.push( function() {
    alert(i);
});

i++;

a.push( function() {
    alert(i);
});

i++;

//condition isn't met, loop terminates

alert(i) //alerts 3 because i is 3 now.
         //That's why all the functions alert 3, because they all 
         //refer to this i and its value is 3

现在你可以这样做（重复删除）：

a.push( function(i){
    return function() {
         alert(i); //Refers to the i passed as argument to the outer function
                   //not the global one
                   //The local i has whatever value the global i had when it was passed
                   //as argument
    };
}(i));
于 2012-08-10T14:46:08.657 回答