我所需要做的就是在当前函数执行结束时执行一个回调函数。
function LoadData()
{
alert('The data has been loaded');
//Call my callback with parameters. For example,
//callback(loadedData , currentObject);
}
这个函数的消费者应该是这样的:
object.LoadData(success);
function success(loadedData , currentObject)
{
//Todo: some action here
}
我怎么实现这个呢?
当前回答
在尝试执行回调函数之前，最好确保它是一个实际的函数:
if (callback && typeof(callback) === "function") {
callback();
}
其他回答
在尝试执行回调函数之前，最好确保它是一个实际的函数:
if (callback && typeof(callback) === "function") {
callback();
}
如果你想在某件事完成时执行一个函数。一个很好的解决方案是监听事件。 例如，我将实现一个Dispatcher，一个DispatcherEvent类与ES6，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')
调度员:
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)
}))
}
}
编码快乐!
p/s:我的代码缺少处理一些错误异常
Try:
function LoadData (callback)
{
// ... Process whatever data
callback (loadedData, currentObject);
}
函数是JavaScript中的第一类;你可以四处传阅。
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);
我希望这个例子能帮助所有想了解JS中回调的人
有些答案虽然正确，但理解起来可能有点棘手。下面是一个外行术语的例子:
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，在使用console.log显示用户列表之前，总是将“Jake”添加到用户中。
源(YouTube)
