在 JavaScript 中创建自定义回调

实际上，您的代码几乎可以按原样工作，只需将回调声明为参数，然后可以使用参数名称直接调用它。

基础知识

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);

这将调用 ，这将调用 ，这将提醒“东西在这里”。doSomethingfoo

请注意，传递函数引用 （） 非常重要，而不是调用函数并传递其结果 （）。在你的问题中，你做得很正确，但值得指出，因为这是一个常见的错误。foofoo()

更高级的东西

有时，您希望调用回调，以便它看到 的特定值。您可以使用 JavaScript 函数轻松做到这一点：thiscall

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`

您还可以传递参数：

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，将要给回调的参数作为数组传递，而不是单独传递，这很有用。您可以使用以下操作：apply

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`

function LoadData(callback) 
{
    alert('the data have been loaded');
    callback(loadedData, currentObject);
}

尝试：

function LoadData (callback)
{
    // ... Process whatever data
    callback (loadedData, currentObject);
}

函数在 JavaScript 中是一流的;你可以把它们传来传去。

在尝试执行回调之前，最好先确保回调是实际函数：

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

  callback();
}

我的 2 美分。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>

   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 !

function loadData(callback) {

    //execute other requirement

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

loadData(function(){

   //execute callback

});

调用回调函数时，我们可以按如下方式使用它：

consumingFunction(callbackFunctionName)

例：

// Callback function only know the action,
// but don't know what's the data.
function callbackFunction(unknown) {
  console.log(unknown);
}

// This is a consuming function.
function getInfo(thenCallback) {
  // When we define the function we only know the data but not
  // the action. The action will be deferred until excecuting.
  var info = 'I know now';
  if (typeof thenCallback === 'function') {
    thenCallback(info);    
  }
}

// Start.
getInfo(callbackFunction); // I know now

这是带有完整示例的 Codepend。

有些答案虽然正确，但可能有点难以理解。这是一个通俗的例子：

var users = ["Sam", "Ellie", "Bernie"];

function addUser(username, callback)
{
    setTimeout(function()
    {
        users.push(username);
        callback();
    }, 200);
}

function getUsers()
{
    setTimeout(function()
    {
        console.log(users);
    }, 100);
}

addUser("Jake", getUsers);

回调意味着，“Jake”始终在显示用户列表之前添加到用户中。console.log

来源 （YouTube）

如果你想在完成某件事时执行一个函数。一个好的解决方案之一是监听事件。 例如，我将用 ES6 实现一个类，然后：DispatcherDispatcherEvent

let Notification = new Dispatcher()
Notification.on('Load data success', loadSuccessCallback)

const loadSuccessCallback = (data) =>{
   ...
}
//trigger a event whenever you got data by
Notification.dispatch('Load data success')

调度：

class Dispatcher{
  constructor(){
    this.events = {}
  }

  dispatch(eventName, data){
    const event = this.events[eventName]
    if(event){
      event.fire(data)
    }
  }

  //start listen event
  on(eventName, callback){
    let event = this.events[eventName]
    if(!event){
      event = new DispatcherEvent(eventName)
      this.events[eventName] = event
    }
    event.registerCallback(callback)
  }

  //stop listen event
  off(eventName, callback){
    const event = this.events[eventName]
    if(event){
      delete this.events[eventName]
    }
  }
}

调度程序事件：

class DispatcherEvent{
  constructor(eventName){
    this.eventName = eventName
    this.callbacks = []
  }

  registerCallback(callback){
    this.callbacks.push(callback)
  }

  fire(data){
    this.callbacks.forEach((callback=>{
      callback(data)
    }))
  }
}

祝您编码愉快！

p/s：我的代码缺少处理一些错误异常

     function login(email, password, callback) {
         //verify the user
         const users = [
          { email: "[email protected]", password: "123" },
          { email: "[email protected]", password: "xyz" }
         ];

         const user = users.find(
           (user) => user.email === email && user.password === password
         );
         callback(user);
       `enter code here`}

    function redirect(user) {
       if (user) {
          //user is successfully logged in
          console.log("user is successfully logged in ");
       } else {
         console.log("Incorrect credentials ");
       } 
    }

    
    login("[email protected]", "123", redirect);

我希望这个例子能帮助到所有想了解JS回调的人