手写一个promise的过程

Posted 2021-09-04 小顺石

const PEDDING = \'PEDDING\';
const RESOLVE = \'RESOLVE\';
const REJECT = \'REJECT\';
// promise 有三种状态
class NewPromise {
// 初始状态为 PEDDING
    status = PEDDING
    result = undefined;
    reason = undefined;
    // 发布订阅者模式
    // 目的是为了实现异步
    onResolveArr = [];
    onRejectArr = [];
    constructor(exc) {
        const resolve = result => {
            if (this.status === PEDDING) {
                this.result = result
                this.status = RESOLVE
                // 执行发布者
                this.onResolveArr.map(fn => fn())
            }
        }
        const reject = reason => {
            if (this.status === PEDDING) {
                this.reason = reason
                this.status = REJECT
                // 执行发布者
                this.onRejectArr.map(fn => fn())
            }
        }
        exc(resolve, reject)

    }

    then(onResolve, onReject) {
        if (this.status === RESOLVE) {
            setTimeout(() => {
                onResolve(this.result)
            }, 0)
        }
        if (this.status === REJECT) {
            setTimeout(() => {
                onReject(this.reason)
            }, 0)
           
        }
        // 发布订阅者模式
        if (this.status === PEDDING) {
            // 将订阅者添加到数组里面
            this.onResolveArr.push(() => {
                onResolve(this.result)
            })
            this.onRejectArr.push(() => {
                this.onReject(this.reason)
            })

        }
    }
}


// let yan = new Promise((resole, reject) => {
//     resole(\'闫大爷真帅\')
// })
// yan.then(res => {
//     console.log(res)
// })

let newYan = new NewPromise((resole, reject) => {
    setTimeout(()=>{
        resole(\'new闫大爷真帅\')
    },3000)
    
})
newYan.then(res => {
    console.log(res)
})

console.log(11111111)