在JavaScript中创建自定义回调

Question

我需要做的就是在当前函数执行结束时执行回调函数.

function LoadData() 
{
    alert('The data has been loaded');
    //Call my callback with parameters. For example,
    //callback(loadedData , currentObject);
}

此功能的消费者应该是这样的:

object.LoadData(success);

function success(loadedData , currentObject) 
{
  //Todo: some action here 
}

我该如何实现？

Answer 1

实际上,您的代码将按原样工作,只需将您的回调声明为参数,您可以使用参数名称直接调用它.

基础

function doSomething(callback) {
    // ...

    // Call the callback
    callback('stuff', 'goes', 'here');
}

function foo(a, b, c) {
    // I'm the callback
    alert(a + " " + b + " " + c);
}

doSomething(foo);

这将打电话doSomething,这将打电话foo,这将提醒"东西在这里".

请注意,传递函数reference(foo)非常重要,而不是调用函数并传递其result(foo()).在你的问题中,你做得很好,但值得指出,因为这是一个常见的错误.

更先进的东西

有时您想要调用回调,以便它看到特定的值this.您可以使用JavaScript call函数轻松完成此操作:

function Thing(name) {
    this.name = name;
}
Thing.prototype.doSomething = function(callback) {
    // Call our callback, but using our own instance as the context
    callback.call(this);
}

function foo() {
    alert(this.name);
}

var t = new Thing('Joe');
t.doSomething(foo);  // Alerts "Joe" via `foo`

你也可以传递参数:

function Thing(name) {
    this.name = name;
}
Thing.prototype.doSomething = function(callback, salutation) {
    // Call our callback, but using our own instance as the context
    callback.call(this, salutation);
}

function foo(salutation) {
    alert(salutation + " " + this.name);
}

var t = new Thing('Joe');
t.doSomething(foo, 'Hi');  // Alerts "Hi Joe" via `foo`

有时,传递您想要将回调作为数组的参数,而不是单独传递是有用的.你可以apply这样做:

function Thing(name) {
    this.name = name;
}
Thing.prototype.doSomething = function(callback) {
    // Call our callback, but using our own instance as the context
    callback.apply(this, ['Hi', 3, 2, 1]);
}

function foo(salutation, three, two, one) {
    alert(salutation + " " + this.name + " - " + three + " " + two + " " + one);
}

var t = new Thing('Joe');
t.doSomething(foo);  // Alerts "Hi Joe - 3 2 1" via `foo`

Answer 2

在尝试执行回调之前,确保回调是实际函数是一种好习惯:

if (callback && typeof(callback) === "function") {

  callback();
}

Answer 3

我2分.相同但不同......

<script>
    dosomething("blaha", function(){
        alert("Yay just like jQuery callbacks!");
    });


    function dosomething(damsg, callback){
        alert(damsg);
        if(typeof callback == "function") 
        callback();
    }
</script>

Answer 4

function loadData(callback) {

    //execute other requirement

    if(callback && typeof callback == "function"){
        callback();
   }
}

loadData(function(){

   //execute callback

});

Answer 5

   function callback(e){
      return e;
   }
    var MyClass = {
       method: function(args, callback){
          console.log(args);
          if(typeof callback == "function")
          callback();
       }    
    }

=============================================

MyClass.method("hello",function(){
    console.log("world !");
});

=============================================

结果是：

hello world !