手寫實現一個promise
function myPromise (callback) {
let self = this;
self.status = 'pending';
self.value = undefined;
self.reason = undefined;
self.fullFiledArr = [];
self.rejectedArr = [];
function resolve (value) {
if(self.status == 'pending') {
self.value = value;
self.status = 'fufilled';
self.fullFiledArr.forEach(function(f) {
f.call(this,self.value)
});
}
}
function reject (reason) {
if(self.status == 'pending') {
self.reason = reason;
self.status = 'rejected';
self.rejectedArr.forEach(function(f) {
f(self.reason)
});
}
}
try{
callback(resolve,reject);
} catch(e) {
reject(e);
}
}
myPromise.prototype.then = function (onFufilled,onRejected) {
let self = this;
let myPromise2;
switch(self.status) {
case 'pending':
myPromise2 = new myPromise(function(resolve,reject) {
self.fullFiledArr.push(function(){
try{
let res = onFufilled(self.value);
if(res instanceof myPromise) {
res.then(resolve,reject);
}
// resolvePromise(myPromise,res);
} catch(e) {
reject(e);
}
})
self.rejectedArr.push(function(){
try{
let res = onRejected(self.reason);
if(res instanceof myPromise) {
res.then(resolve,reject);
}
} catch(e) {
reject(e);
}
})
});
break;
case 'fufilled':
myPromise2 = new myPromise(function(resolve,reject) {
try{
let res = onFufilled(self.value);
if(res instanceof myPromise) {
res.then(resolve,reject);
}
} catch(e) {
reject(e);
}
});
break;
case 'rejected':
myPromise2 = new myPromise(function(resolve,reject) {
try{
let res = onRejected(self.reason);
if(res instanceof myPromise) {
res.then(resolve,reject);
}
} catch(e) {
reject(e);
}
})
}
return myPromise2;
}
function resolvePromise(promise,x,resolve,reject){
if(promise===x){
throw new TypeError("type error")
}
let isUsed;
if(x!==null&&(typeof x==="object"||typeof x==="function")){
try{
let then=x.then;
if(typeof then==="function"){
//是一個promise的情況
then.call(x,function(y){
if(isUsed)return;
isUsed=true;
resolvePromise(promise,y,resolve,reject);
},function(e){
if(isUsed)return;
isUsed=true;
reject(e);
})
}else{
//僅僅是一個函式或者是物件
resolve(x)
}
}catch(e){
if(isUsed)return;
isUsed=true;
reject(e);
}
}else{
//返回的基本型別，直接resolve
resolve(x)
}
}
const async1 = () => {
var p = new myPromise((resolve,reject)=> {
console.log('1');
setTimeout(()=>{
resolve('鏈式呼叫1');
},1000)
})
return p;
}
const async2 = () => {
var p = new myPromise((resolve,reject)=> {
console.log('2');
setTimeout(()=>{
resolve('鏈式呼叫2');
},1000)
})
return p;
}
async1().then((data) => {
console.log(data);
return async2();
}).then((data)=>{
console.log(data);
})