??
new Promise((resolve, reject) => {
//??????resolve?????reject
}).then((res) => {
//resolve???????????
}, (err) => {
//reject???????????
}).then(res => {
//????then????????promise
//??????????
}).catch(reason => {
});
//?????promise?????then?
//?????????????catch
Promise.all([promise1, ...]).then();
??????????
????Promise?
1.????????pending?, ‘fulfilled’, ‘rejected’
2.????then???????????
//promise.js
class Promise{
//?????????
constructor(excutorCallBack){
this.status = 'pending';
this.value = undefined;
this.fulfillAry = [];
this.rejectedAry = [];
//=>??Excutor
let resolveFn = result => {
if(this.status !== 'pending') return;
let timer = setTimeout(() => {
this.status = 'fulfilled';
this.value = result;
this.fulfillAry.forEach(item => item(this.value));
}, 0);
};
let rejectFn = reason => {
if(this.status !== 'pending')return;
let timer = setTimeout(() => {
this.status = 'rejected';
this.value = reason;
this.rejectedAry.forEach(item => item(this.value))
})
};
try{
//????????
excutorCallBack(resolveFn, rejectFn);
} catch(err) {
//=>???????rejected????
rejectFn(err);
}
}
then(fulfilledCallBack, rejectedCallBack) {
//resolve?reject???????????
//??????????????then???????
this.fulfillAry.push(fulfilledCallBack);
this.rejectedAry.push(rejectedCallBack);
//??push???????
}
}
module.exports = Promise;
?????????
let Promise = require('./promise');
let p1 = new Promise((resolve, reject) => {
setTimeout(() => {
Math.random()<0.5?resolve(100):reject(-100);
}, 1000)
}).then(res => {
console.log(res);
}, err => {
console.log(err);
})
?????? ??????
?????????????????????then??????
//then??????
then(fulfilledCallBack, rejectedCallBack) {
//???????
typeof fulfilledCallBack !== 'function' ? fulfilledCallBack = result => result:null;
typeof rejectedCallBack !== 'function' ? rejectedCallBack = reason => {
throw new Error(reason instanceof Error? reason.message:reason);
} : null
//????Promise??????????Promise?
return new Promise((resolve, reject) => {
//????this?????Promise????????Promise
//?????,????
//???Promise(????return??Promise)?resolve?reject???????????
//??????????????then???????
this.fulfillAry.push(() => {
try {
//?then??????????
//?????????
let x = fulfilledCallBack(this.value);
//?????????????????????????Promise????
//?????x???Promise??????then??
//????Promise,?????Promise?resolve??,
//?Promise?fulfilAry????,??Promise?then???.?Promise?resolve??
x instanceof Promise ? x.then(resolve, reject):resolve(x);
}catch(err){
reject(err)
}
});
//????
this.rejectedAry.push(() => {
try {
let x = this.rejectedCallBack(this.value);
x instanceof Promise ? x.then(resolve, reject):resolve(x);
}catch(err){
reject(err)
}
})
}) ;
}
?????????
let p1 = new Promise((resolve, reject) => {
setTimeout(() => {
Math.random()<0.5?resolve(100):reject(-100);
}, 1000)
})
let p2 = p1.then(result => {
//??then????????Promise
return result + 100;
})
let p3 = p2.then(result => {
console.log(result);
}, reason => {
console.log(reason)
})
???????????????????????
??then???catch?????????
catch(rejectedCallBack) {
return this.then(null, rejectedCallBack);
}
??????Promise.all()
?????Promise.all()
//???????????????
static all(promiseAry = []) {
let index = 0,
result = [];
return new Promise((resolve, reject) => {
for(let i = 0; i < promiseAry.length; i++){
promiseAry[i].then(val => {
index++;
result[i] = val;
if( index === promiseAry.length){
resolve(result)
}
}, reject);
}
})
}
??????Promise.race()
????race??
static race(promises) {
return new Promise((resolve, reject) => {
if (promises.length === 0) {
return;
} else {
for(let i = 0; i < promises.length; i++){
promises[i].then(val => {
resolve(result);
return;
}
}, reject);
}
}
});
}
??????Promise.resolve()
static resolve (value) {
if (value instanceof Promise) return value
return new Promise(resolve => resolve(value))
}
??????Promise.reject()
static reject (value) {
return new Promise((resolve, reject) => reject(value))
}
????????
?????????????????Promise???????
class Promise{
constructor(excutorCallBack){
this.status = 'pending';
this.value = undefined;
this.fulfillAry = [];
this.rejectedAry = [];
//=>??Excutor
let resolveFn = result => {
if(this.status !== 'pending') return;
let timer = setTimeout(() => {
this.status = 'fulfilled';
this.value = result;
this.fulfillAry.forEach(item => item(this.value));
}, 0);
};
let rejectFn = reason => {
if(this.status !== 'pending')return;
let timer = setTimeout(() => {
this.status = 'rejected';
this.value = reason;
this.rejectedAry.forEach(item => item(this.value))
})
};
try{
excutorCallBack(resolveFn, rejectFn);
} catch(err) {
//=>???????rejected????
rejectFn(err);
}
}
then(fulfilledCallBack, rejectedCallBack) {
typeof fulfilledCallBack !== 'function' ? fulfilledCallBack = result => result:null;
typeof rejectedCallBack !== 'function' ? rejectedCallBack = reason => {
throw new Error(reason instanceof Error? reason.message:reason);
} : null
return new Promise((resolve, reject) => {
this.fulfillAry.push(() => {
try {
let x = fulfilledCallBack(this.value);
x instanceof Promise ? x.then(resolve, reject ):resolve(x);
}catch(err){
reject(err)
}
});
this.rejectedAry.push(() => {
try {
let x = this.rejectedCallBack(this.value);
x instanceof Promise ? x.then(resolve, reject):resolve(x);
}catch(err){
reject(err)
}
})
}) ;
}
catch(rejectedCallBack) {
return this.then(null, rejectedCallBack);
}
static all(promiseAry = []) {
let index = 0,
result = [];
return new Promise((resolve, reject) => {
for(let i = 0; i < promiseAry.length; i++){
promiseAry[i].then(val => {
index++;
result[i] = val;
if( index === promiseAry.length){
resolve(result)
}
}, reject);
}
})
}
static race(promiseAry) {
return new Promise((resolve, reject) => {
if (promiseAry.length === 0) {
return;
}
for (let i = 0; i < promiseAry.length; i++) {
promiseAry[i].then(val => {
resolve(val);
return;
}, reject);
}
})
}
static resolve (value) {
if (value instanceof Promise) return value
return new Promise(resolve => resolve(value))
}
static reject (value) {
return new Promise((resolve, reject) => reject(value))
}
}
module.exports = Promise;
