SOURCE

class MyPromise {
    constructor(executor) {
        this.status = 'pending'
        this.value = null
        this.reason = null
        this.onFulfilledArray = []
        this.onRejectedArray = []

        const resolve = (value) => {
            // if (value instanceof Promise) {
            //     return value.then(resolve, reject)
            // }
            // 定义promise队列此实现方法并不稳定
            setTimeout(() => {
                this.value = value
                this.status = 'fulfilled'
                this.onFulfilledArray.forEach(func =>{
                    console.log(func)
                    func(value)
                })
            })

        }

        const reject = (reason) => {
            // 定义promise队列此实现方法并不稳定
            setTimeout(() => {
                this.reason = reason
                this.status = 'rejected'
                this.onRejectedArray.forEach(func => func(this.reason))
            })

        }

        try {
            executor(resolve, reject)
        } catch (e) {
            reject(e)
        }

    }
    then(onfulfilled, onrejected) {

        // onfulfilled = typeof onfulfilled === 'function' ? onfulfilled : data => data
        // onrejected = typeof onrejected === 'function' ? onrejected : error => error
        // if (this.status === 'pending') {
        //     this.onfulfilledArray.push(onfulfilled)
        //     this.onfulfilledArray.push(onrejected)
        // }
        // if (this.status === 'fulfilled') {
        //     this.value = onfulfilled(this.value)
        // }
        // if (this.status === 'rejected') {
        //     onrejected(this.reason)
        // }
        // return this

        onfulfilled = typeof onfulfilled === 'function' ? onfulfilled : data => data
        onrejected = typeof onrejected === 'function' ? onrejected : error => error

        // promise2 将作为 then 方法的返回值
        let promise2
        if (this.status === 'fulfilled') {
         return   promise2 = new Promise((resolve, reject) => {
                setTimeout(() => {
                    try {
                        // 这个新的 promise2 resolved 的值为 onfulfilled 的执行结果
                        let result = onfulfilled(this.value)
                        resolve(result)
                    }
                    catch (e) {
                        reject(e)
                    }
                })
            })
        }
        if (this.status === 'rejected') {
          return  promise2 = new Promise((resolve, reject) => {
                setTimeout(() => {
                    try {
                        // 这个新的 promise2 reject 的值为 onrejected 的执行结果
                        let result = onrejected(this.value)
                        resolve(result)
                    }
                    catch (e) {
                        reject(e)
                    }
                })
            })
        }
        if (this.status === 'pending') {
         return   promise2 = new Promise((resolve, reject) => {
                this.onFulfilledArray.push(() => {
                    try {
                        let result = onfulfilled(this.value)
                        resolve(result)
                    }
                    catch (e) {
                        reject(e)
                    }
                })

                this.onRejectedArray.push(() => {
                    try {
                        let result = onrejected(this.reason)
                        resolve(result)
                    }
                    catch (e) {
                        reject(e)
                    }
                })
            })
        }

      
    }
}



const promise = new MyPromise((resolve, reject) => {
    setTimeout(() => {
        resolve('data')
    }, 1000)

    // resolve('data')
    //reject('error')
})

promise
    .then((data) => {
        console.log(data)
        return data + '+next'
    })
    .then(data => {
        console.log(data)
    })