ES6 手写Promise
class MyPromise {
value = undefined
status = 'pending'
constructor(resolver) {
let resolve = (val) => {
this.status = 'resolved'
this.value = val
}
let reject = (val) => {
this.status = 'resolved'
this.value = val
}
resolver(resolve, reject)
}
then = (callbackResolve, callbackReject) => {
if(callbackResolve && this.status === 'resolved') {
callbackResolve(this.value)
} else if(callbackResolve && (this.status === 'rejected' || this.status === 'pending')) {
callbackResolve(this.value)
}
return this
}
catch = (callbackReject) => {
if(callbackReject && this.status === 'rejected') {
callbackReject(this.value)
}
}
static resolve = (value) => {
if (value instanceof this) return value
return new this(resolve => resolve(value))
}
static reject = (reason) => {
return new this((_, reject) => reject(reason))
}
static all = (promises) => {
let count = 0
let values = new Array(promises.length)
return new this((resolve, reject) => {
promises.forEach((promise, index) => {
this.resolve(promise).then(value => {
count++
values[index] = value
if (count === promises.length) resolve(values)
}, reason => reject(reason))
})
})
}
static race = (promises) => {
return new this((resolve, reject) => {
promises.forEach(promise => {
this.resolve(promise).then(value => resolve(value))
}, reason => reject(reason))
})
}
}
Promise.resolve('Promise').then(res => {console.log(res)})
MyPromise.resolve('MyPromise').then(res => {console.log(res)})
