const PENDING = 'PENDING';
const FULFILLED = 'FULFILLED';
const REJECTED = 'REJECTED';
class Promise {
constructor(executor) {
//resolve reject
this.status = PENDING;
this.value = undefined;
this.reason = undefined;
// 存放成功的回调
this.onResolvedCallbacks = [];
// 存放失败的回调
this.onRejectedCallbacks= [];
let resolve = (value) => {
if(this.status === PENDING) {
this.status = FULFILLED;
this.value = value;
// 依次将对应的函数执行
this.onResolvedCallbacks.forEach(fn=>fn());
}
}
let reject = (reason) => {
if(this.status === PENDING) {
this.status = REJECTED;
this.reason = reason;
// 依次将对应的函数执行
this.onRejectedCallbacks.forEach(fn=>fn());
}
}
try {
executor(resolve,reject)
} catch (error) {
reject(error)
}
}
then(onFulfilled, onRejected) {
if (this.status === FULFILLED) {
onFulfilled(this.value)
}
if (this.status === REJECTED) {
onRejected(this.reason)
}
if (this.status === PENDING) {
// 如果promise的状态是 pending,需要将 onFulfilled 和 onRejected 函数存放起来,等待状态确定后,再依次将对应的函数执行
this.onResolvedCallbacks.push(() => {
onFulfilled(this.value)
});
// 如果promise的状态是 pending,需要将 onFulfilled 和 onRejected 函数存放起来,等待状态确定后,再依次将对应的函数执行
this.onRejectedCallbacks.push(()=> {
onRejected(this.reason);
})
}
}
}
const promise = new Promise((resolve,reject)=>{
setTimeout(()=>{
resolve("成功");
},1000)
}).then(
(data)=>{
console.log("success",data)
},
(error)=>{
console.log("error",error)
}
)
console