在javascript中等待回调 [英] Wait for callback in javascript

问题描述

我正在尝试创建一个函数，该函数返回一个带有回调信息的对象:

I'm trying to create a function that returns a object with information of a callback:

var geoloc;

var successful = function (position) {
    geoloc = {
        longitude: position.coords.longitude,
        latitude: position.coords.latitude
    };
};

var getLocation = function () {
    navigator.geolocation.getCurrentPosition(successful, function () {
        alert("fail");
    });

    return geoloc;
};

我该怎么做?函数 getLocation 在 successful 执行前返回空值.

How can I do this? The function getLocation return null value before successful is executed.

谢谢！

推荐答案

使用回调是因为函数是异步的.回调会在未来的某个时间点运行.

Callbacks are used because the function is asynchronous. The callback runs at some point in the future.

所以，是的 getLocation 在回调被触发之前返回.这就是异步方法的工作原理.

So, yes getLocation returns before the callback is triggered. That's how asynchronous methods work.

你不能等待回调，这不是它的工作方式.您可以向 getLocation 添加回调，该回调在完成后运行.

You cannot wait for the callback, that's not how it works. You can add a callback to getLocation, that runs once it's done.

var getLocation = function(callback){
    navigator.geolocation.getCurrentPosition(function(pos){
        succesfull(pos);
        typeof callback === 'function' && callback(geoloc);
    }, function(){
        alert("fail");
    });
};

现在不是执行 var x = getLocation() 并期望返回值，您可以这样调用它:

Now instead of doing var x = getLocation() and expecting a return value, you call it like this:

getLocation(function(pos){
    console.log(pos.longitude, pos.latitude);
});

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