promise 是为了解决回调地狱的问题。
主要有以下几个方法
- Promise.prototype.then
- Promise.prototype.catch
- Promise.all
- Promise.race
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| const log = console.log.bind(console)
class BananasPromise {
constructor(func) {
if(typeof func !== 'function') {
throw new Error(func, 'is no a function')
}
this.func = func
this.state = 'init'
const resolve = this.resolve.bind(this)
const reject = this.reject.bind(this)
const r = () => {
func(resolve, reject)
return this
}
return r
}
_efunc() {
}
then(done) {
this.done = done || this._efunc
if(this.state === 'done') {
done(this.args)
}
return this
}
catch(fail) {
this.fail = fail || this._efunc
if(this.state === 'fail') {
fail(this.err)
}
}
resolve(args='') {
this.state = 'done'
this.args = args
this.done && this.then(this.done)
}
reject(args='') {
this.state = 'fail'
this.err = args
this.catch && this.catch(this.fail)
}
static _init() {
const cls = this
cls.state = 'init'
cls.done = () => {}
cls.fail = () => {}
cls._resule = []
cls._err = null
}
static all(array) {
const cls = this
let len = array.length
cls._init()
array.forEach((i, index) => {
if(cls._err !== null) {
return
}
i().then((a) => {
if(cls._err !== null) {
return
}
len--
cls._resule[index] = a
if(len === 0) {
cls.state = 'done'
cls.then()
}
}).catch((err) => {
if(cls._err !== null) {
return
}
cls.state = 'fail'
cls._err = err
cls.catch()
})
})
return this
}
static then(done) {
const cls = this
if(this.state === 'done') {
cls.done(cls._resule)
} else if(this.state === 'init') {
cls.done = done || cls.done
}
return this
}
static catch(fail) {
const cls = this
if(cls.state === 'fail') {
cls.fail(cls._err)
} else if(cls.state === 'init') {
cls.fail = fail || cls.fail
}
}
static race(array) {
const cls = this
cls._init()
array.forEach((item) => {
if(cls.state === 'done' || cls.state === 'fail') {
return
}
item().then((data) => {
if(cls.state === 'done' || cls.state === 'fail') {
return
}
cls.state = 'done'
cls._resule = data
cls.then()
}).catch((err) => {
if(cls.state === 'done' || cls.state === 'fail') {
return
}
cls.state = 'fail'
cls._err = err
cls.catch()
})
})
return cls
}
}
|