使 JavaScript 方法等待构造函数完成 [英] Make JavaScript method wait for constructor to complete

问题描述

构造函数需要一些时间，在调用方法时，this.folders 尚未定义.如何让 getIt() 等到构造函数完成?

The constructor takes some time, and when the method is called, this.folders is not yet defined. How do I allow getIt() to wait until the constructor is complete?

function test() {
    var t=this;
    $.getJSON('~.php?task=getFolders&dummy='+new Date().getTime(), function(returned){
        t.folders=returned;
    });
}
test.prototype.getIt = function() {
    return this.folders;
};

var myObj = new test();
console.log(myObj.getIt());

推荐答案

由于 $.getJSON() 是异步的，所以没有办法阻止 test() 从填充 t.folders 后返回.

Since $.getJSON() is asynchronous, there is no way of preveting test() from returning after t.folders is populated.

您可以使用回调:

function test(callback) {
    $.getJSON('~.php?task=getFolders&dummy='+new Date().getTime(), function(returned){
        callback(returned);
    });
}

var myObj = new test(function (folders) {
    console.log(folders);
});

或者一个承诺(在这个例子中，使用 Q 库):

Or a promise (in this example, using Q library):

function test() {
    var t = this;
    t.folders = Q.defer();

    $.getJSON('~.php?task=getFolders&dummy='+new Date().getTime(), function(returned){
        t.folders.resolve(returned);
    });
}
test.prototype.getIt = function() {
    return this.folders.promise;
};

var myObj = new test();
myObj.getIt().done(function (folders) {
    console.log(folders);
});

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