立即用AngularJS返回承诺解决 [英] Immediately return a resolved promise using AngularJS

问题描述

我试图让我周围的承诺的头在JavaScript中（尤其是AngularJS）。

I'm trying to get my head around promises in JavaScript (in particular AngularJS).

我有一个服务功能，我们称之为 FooService接口，如果我们已经加载了一些数据来检查。如果有，我只是希望它回归了，如果我们没有，我们需要加载数据并返回一个承诺：

I have a function in a service, let's call it fooService, that checks if we've loaded some data. If it has, I just want it to return, and if we haven't, we need to load the data and return a promise:

this.update = function(data_loaded) {
    if (data_loaded) return;  // We've loaded the data, no need to update

    var promise = Restangular.all('someBase').customGet('foo/bar').then(function(data) {
        // Do something with the data here
    }

    return promise;
}

我有另一个函数，然后调用更新 FooService接口像这样的功能：

fooService.update(data_loaded).then(function() {
    // Do something here when update is finished
})

我在这里的问题是，如果我们不需要加载数据在更新函数，承诺不退还，因此。然后（）不在我的其他函数调用。应该采取什么办法在这里 - 基本上我想从更新立即返回一个解决的承诺（）函数，如果我们不需要从Restangular调用获取数据

My issue here is that if we don't need to load the data in the update function, a promise isn't returned, so the .then() is not called in my other function. What should the approach be here - basically I want to return a resolved promise immediately from the update() function if we do not need to get data from the Restangular call?

推荐答案

目前接受的答案是过于复杂，滥用<一个href=\"http://stackoverflow.com/questions/23803743/what-is-the-deferred-anti-pattern-and-how-do-i-avoid-it\">deferred反面模式的。这里有一个简单的方法：

The current accepted answer is overly complicated, and abuses the deferred anti pattern. Here is a simpler approach:

this.update = function(data_loaded) {
    if (data_loaded) return $q.when(data);  // We've loaded the data, no need to update

    return Restangular.all('someBase').customGet('foo/bar')
                             .then(function(data) {
        // Do something with the data here 
    });
};

或者，更进一步：

this._updatep = null;
this.update = function(data_loaded) { // cached
    this._updatep = this._updatep || Restangular.all('someBase') // process in
                                                .customGet('foo/bar'); //.then(..
    return this._updatep;
};

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