我所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);
}
object.LoadData(success);
function success(loadedData , currentObject)
{
//Todo: some action here
}
我该如何实现这个功能？
实际上，你的代码基本上可以直接使用，只需将回调函数声明为一个参数，并使用该参数名称直接调用即可。
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);
这会调用doSomething函数，然后调用foo函数，最终弹出"stuff goes here"。
需要注意的是，传递函数时非常重要要传递函数引用（foo），而不是调用函数并传递其结果（foo()）。在您的问题中，您做得很好，但值得指出的是，这是一个常见错误。
有时候您想要调用回调函数以便它看到this的特定值。您可以使用JavaScript的call函数轻松实现：
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`
apply来实现这个功能：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`
setTimeout()。答案是将回调函数包装在闭包中：doSomething(function(){foo('this','should','work')})。 - slebetman在尝试执行回调函数之前，确保回调函数是实际的函数是一个好的实践：
if (callback && typeof(callback) === "function") {
callback();
}
typeof callback == "function"，将会得到相同的结果。 - Reactgularcallback && 的意义所在。 - theonlygusti我的两分钱。同样但不同...
<script>
dosomething("blaha", function(){
alert("Yay just like jQuery callbacks!");
});
function dosomething(damsg, callback){
alert(damsg);
if(typeof callback == "function")
callback();
}
</script>
function loadData(callback) {
//execute other requirement
if(callback && typeof callback == "function"){
callback();
}
}
loadData(function(){
//execute callback
});
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 !
有些答案虽然正确，但可能有点难以理解。以下是一个通俗易懂的例子：
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);
console.log显示用户列表之前，总是将“Jake”添加到用户中。
如果你想在某个操作完成时执行一个函数，监听事件是一个很好的解决方案。
例如，我将使用ES6实现一个Dispatcher，一个DispatcherEvent类，然后：
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')
调度程序：
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]
}
}
}
DispatcherEvent:
class DispatcherEvent{
constructor(eventName){
this.eventName = eventName
this.callbacks = []
}
registerCallback(callback){
this.callbacks.push(callback)
}
fire(data){
this.callbacks.forEach((callback=>{
callback(data)
}))
}
}
愉快地编码吧！
附言：我的代码缺少处理一些错误异常的部分。
在调用回调函数时，我们可以像下面这样使用它:
consumingFunction(callbackFunctionName)
例子:
// 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
这是一个带有完整示例的Codepend。
function login(email, password, callback) {
//verify the user
const users = [
{ email: "abc@gmail.com", password: "123" },
{ email: "xyz@gmail.com", 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("abc@gmail.com", "123", redirect);
function LoadData(callback)
{
alert('the data have been loaded');
callback(loadedData, currentObject);
}
function success后才能调用object.LoadData(success)。否则，你会收到一个错误提示，告诉你该函数未定义。 - J. Bruni