JavaScript的似乎并不等待返回值 [英] JavaScript doesn't seem to wait for return values

问题描述

我一直在挣扎了一会儿。我是新来的Javascript，并已使code我已经写了异步运行IM pression下。这是一个普通的例子：

I've been struggling with this for a while now. I'm new to Javascript, and have been under the impression that the code I've been writing has been running asynchronously. Here is a generic example:

我运行功能的一些code。功能A然后调用函数B，谁需要一个变量回归A因此A可以在以后的操作中使用它。看来虽然当A呼叫B时，它仍继续运行它自己的code，不等待阻塞其返回值，以及B是不够快使得A结束到达那里将需要对点使用返回值，我得到的未定义的变量类型错误。

I run some code in function a. Function A then calls Function B, who needs to return a variable to A so A can use it in its later operations. It seems though that when A calls B, it still continues to run its own code, not waiting blocked for its return value, and B isn't fast enough such that A ends up reaching the point where it would have needed to use the return value and I get an undefined variable type error.

我身边有这样的工作方式是有函数的调用函数B，然后调用一个函数C，会做什么，以后的操作是A将与返回值做....我是那种序列化的我通过电话，而不是收益code ......这很麻烦，虽然...

The way I have worked around this is have function A call Function B which then calls a Function C that would do what the later operations that A would be doing with the return value....I'm kind of serializing my code through calls instead of returns...that is cumbersome though...

下面是当它在实际code发生的例子：

Here is an example of when it happens in actual code:

function initialize() {
    //Geocode Address to obtin Lat and Long coordinates for the starting point of our map
    geocoder = new google.maps.Geocoder();
    var results = geocode(geocoder);
    makeMap(results[0].geometry.location.lat(), results[0].geometry.location.lng());

}

function geocode(geocoder) {
    //do geocoding here...

    var address = "3630 University Street, Montreal, QC, Canada";
    geocoder.geocode({ 'address': address }, function (results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
           return results;
            }
         else {
            alert("Geocode was not successful for the following reason: " + status);
        }
   });

}

function makeMap(lat, long) {
  //  alert(lat); for debuging
    var mapOptions = {
        center: new google.maps.LatLng(lat, long),
        zoom: 17,
        mapTypeId: google.maps.MapTypeId.ROADMAP
    };
     map = new google.maps.Map(document.getElementById("map_canvas"),
        mapOptions);
}

注意：初始化得到由身体的onload =叫初始化（）在我的HTML

Note: initialize gets called by body onload="initialize()" in my html.

所以，问题是，makeMap需要由地理code函数获得的纬度和经度值，但我在控制台说结果得到一个错误是不确定的。到底是怎么回事？我从Java来了，所以我有点困惑的数据流是如何发生在这里的JS！这将是未来的宝贵经验！

So the issue is that the makeMap requires the lat and longitude values obtained by the Geocode function, but I get an error in the console saying results is undefined. What is going on? I came from Java so I'm a little confused about how data flow is happening here in JS! This will be valuable lessons for the future!

在一个侧面的问题：如何，我应该在整个外部脚本拆我的功能呢？什么是好的做法？应我的所有功能塞进一个外部.js文件或者我应该像组功能于一体？

On a side question: How should I split my functions across external scripts? What is considered good practice? should all my functions be crammed into one external .js file or should I group like functions together?

推荐答案

您似乎有问题有很好的理解，但它听起来像是你不熟悉的，解决的方式。解决这一问题的最普通的方式是通过使用一个回调。这基本上是异步的方式来等待一个返回值。这里是你怎么能在你的情况下使用它：

You seem to have a good understanding of the problem, but it sounds like you aren't familiar with the way to solve it. The most common way to address this is by using a callback. This is basically the async way to wait for a return value. Here's how you could use it in your case:

function initialize() {
    //Geocode Address to obtin Lat and Long coordinates for the starting point of our map
    geocoder = new google.maps.Geocoder();
    geocode(geocoder, function(results) {
        // This function gets called by the geocode function on success
        makeMap(results[0].geometry.location.lat(), results[0].geometry.location.lng());        
    });
}

function geocode(geocoder, callback) {
    //do geocoding here...

    var address = "3630 University Street, Montreal, QC, Canada";
    geocoder.geocode({ 'address': address }, function (results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            // Call the callback function instead of returning
            callback(results);
        } else {
            alert("Geocode was not successful for the following reason: " + status);
        }
   });

}

...

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