Variable scope in anonymous function

Question

I'm trying to populate an array in JavaScript using an anonymous function in the jQuery getJSON() function as follows.

$(document).ready(function() {

    function Link(url, title) {
        this.url = url;
        this.title = title;
    }
    var links = [];

    $.getJSON("http://reddit.com/r/programming/.json?jsonp=?", function(data) {
        $.each(data.data.children, function(i, item) {
            var title = item.data.title;
            var url = item.data.url;

            links.push(new Link(url, title));
        })
    });

    for(var i=0; i< links.length; i++) {
        var output = "<a href='" + k + "'>" + links[k] + "</a>";
        $('<p>' + link + '</p>').appendTo('#content');
    }

});

But, when I hit the for loop, the links array shows up empty. What's going on here?

Answer 1

Try that :

    $(document).ready(function() {

        function Link(url, title) {
            this.url = url;
            this.title = title;
        }

        $.getJSON("http://reddit.com/r/programming/.json?jsonp=?", function(data) {
            var links = [];
            $.each(data.data.children, function(i, item) {
                var title = item.data.title;
                var url = item.data.url;

                links.push(new Link(url, title));
            })
            for(var i=0; i< links.length; i++) {
                var output = "<a href='" + k + "'>" + links[k] + "</a>";
                $('<p>' + link + '</p>').appendTo('#content');
            }
        });


    });

Your loop was probably executed before your callback ;)

Answer 2

That's because $.getJSON is an asynchronous method. The code execution continues even after $.getJSON and reaches the for loop, by which time, your async request hasn't completed yet. You should move the loop within $.getJSON .

Answer 3

此jsFiddle http://jsfiddle.net/cArYg/2/显示了在getJson回调之前发生的迭代