手写实现一个Promise

骑猪看日落 2022-02-22 16:46 325阅读 0赞

function NewPromise (fn) {
    
        this.state = 'pending'
        this.fulfillList = []
        this.rejectList = []
    
        fn(this.resolve.bind(this), this.reject.bind(this))
        // 成功执行成功的队列
    }
    
    NewPromise.prototype.resolve = function (data) {
    
        this.state = 'fulfilled'
        var args = [].slice.call(arguments)
    
        setTimeout(function() {
    
            this.fulfillList.forEach(function ( itemFn, key, arr) {
                itemFn.apply(null, args)
                arr.shift()
            })
    
        }.bind(this), 0)
    } //失败 执行失败的队列
    
    NewPromise.prototype.reject = function (data) {
    
        this.state = 'rejected'
        var args2 = [].slice.call(arguments)
    
        setTimeout(function() {
    
            this.rejectList.forEach(function ( itemFn, key, arr) {
                itemFn.apply(null, args2)
                arr.shift()
    
            })
    
        }.bind(this), 0)
    }
    //成功的回调函数
    
    NewPromise.prototype.done = function (handle) {
    
        if(typeof handle === 'function') {
            this.fulfillList.push(handle)
    
        } else {
    
            throw new Error('回调出错')
            return this
    
        }
    }
    
    // 失败的回调函数
    NewPromise.prototype.fail = function (handle) {
    
        if(typeof handle === 'function') {
    
            this.rejectList.push(handle)
    
        } else {
    
            throw new Error('回调出错')
            return this
    
        }
    }
    
    NewPromise.prototype.then = function (fulfiil, reject) {
    
        this.done( fulfill ) || function () {}
        .fail(reject) || function () {}
        return this
    
    }
    
    NewPromise.prototype.always = function (handle) {
    
        this.done(handle) || function () {}
        .fail(handle) || function () {}
        return this
    
    }
    
    var prm = NewPromise(function (resolve, reject) {
    
        setTimeout(function () {
                resolve('成功的参数')
                reject('失败的参数')
        }, 1000)
    })
    prm.then(function (data) {
        console.log(data)
    }).fail(function (data) {
        console.log(data)
    })