处理延迟对象数组 [英] Dealing with Arrays of Deferred Objects

问题描述

自从使用$.Deferred以来，我已经遇到过几次这种情况:我有一个值列表，每个值都以某种方式产生一个Deferred Object，我想在所有Deferred Objects被解析后执行一个回调.

Since using $.Deferred I've run into this scenario a couple times: I have a list of values each of which yields a Deferred Object in some way and I want to execute a callback once all of the Deferred Objects are resolved.

一个更具体的例子是这样的:

A more concrete example would be something like this:

var urls = [ 'foo.com', 'bar.com', 'baz.com', 'qux.com' ],
    defers = [], defer;

for( var i = 0, j = urls.length; i < j; i++ ){
    defer = $.ajax({
        url: 'http://' + urls[ i ]
    });

    defers.push(defer);
}

$.when.apply(window, defers).done(function(){
    // Do Something
});

是否有比示例中的代码更优雅的解决方案?

Is there a more elegant solution than the code in my example?

推荐答案

写此示例的一种更优雅的方法是使用数组映射函数(或jQuery的$ .map):

A more elegant way to write this example is with the array map function (or jQuery's $.map):

var urls = [ 'foo.com', 'bar.com', 'baz.com', 'qux.com' ];

var defers = urls.map( function( url) {
    return $.ajax({
        url: 'http://' + url
    });
});

$.when.apply(window, defers).done(function(){
    // Do Something
});

您甚至可以滚动自己的"whenDone"和"fetchURL"功能:

You could even roll your own "whenDone" and "fetchURL" functions:

Array.prototype.whenDone = function(callback){
    return $.when.apply(window, this).done(callback);
}

function fetchURL(url){
    return $.ajax({
        url: 'http://' + url
    });
}

var urls = [ 'foo.com', 'bar.com', 'baz.com', 'qux.com' ];    

urls.map( fetchUrl ).whenDone(function(){
    // Do Something
});

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