如何让jQuery的等待一个函数来执行另一个函数之前完成？ [英] How can I make jquery wait for one function to finish before executing another function?

问题描述

function test(){
var distance=null;
       first();
       second();
       third();
alert(distance);//it shows null always because it take 2 second to complete.

}
 function first(tolat, tolon, fromlat,fromlon){

// calulating road distance between two points on the map using any other distance caluculating apis. 

distance=dis;  // update the value of distance but it takes 2 second to complete.

}
 function second(){}
 function third(){}

我有这种情况在我的code，现在很多时间功能前三第一和第二完成执行和距离值不更新被调用。

i have this type of situation in my code, now many time function three is called before first and second complete execution and distance value is not updated.

推荐答案

请利用回调的：

function first(tolat, tolon, fromlat, fromlon, callback) {
     if (typeof(callback) == 'function') {
        callback(distance);
     }
}

function second() { }
function third() { }

first("vartolat", "vartolon", "varfromlat", "varfromlon", function(distance) {
    alert(distance);
    second();
    third();
});

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