8.错误处理

// 错误捕获
const PENDING = 'pending'
const FUFILLED = 'fulfilled'
const REJECTED = 'rejected'

class MyPromise {
    constructor (executor) {
        // 执行器 错误捕获处理
        try {
            executor(this.resolve, this.reject)
        } catch (error) {
            this.reject(error)
        }
    }
    status = PENDING
    value = undefined
    reason = undefined
    successCallback = []
    failCallback = []

    resolve = value => {
        if (this.status !== PENDING) return
        this.status = FUFILLED
        this.value = value
        while(this.successCallback.length) this.successCallback.shift()()
    }
    reject = reason => {
        if (this.status !== PENDING) return
        this.status = REJECTED
        this.reason = reason
        while(this.failCallback.length) this.failCallback.shift()()
    }
    then(successCallback, failCallback) {
        const promise2 = new MyPromise((resolve, reject) => {
            if (this.status === FUFILLED) {
                setTimeout(() => {
                    // 成功回调 错误捕获处理
                    try {
                        const successValue = successCallback(this.value)
                        resolvePromise(promise2, successValue, resolve, reject)
                    } catch (error) {
                        reject(error)
                    }
                }, 0)
            } else if (this.status === REJECTED) {
                setTimeout(() => {
                    // 失败回调 错误捕获处理
                    try {
                        const failReason = failCallback(this.reason)
                        resolvePromise(promise2, failReason, resolve, reject)
                    } catch (error) {
                        reject(error)
                    }
                }, 0)
            } else {
                this.successCallback.push(() => {
                    setTimeout(() => {
                        // 成功回调 错误捕获处理
                        try {
                            const successValue = successCallback(this.value)
                            resolvePromise(promise2, successValue, resolve, reject)
                        } catch (error) {
                            reject(error)
                        }
                    }, 0)
                })
                this.failCallback.push(() => {
                    setTimeout(() => {
                        // 失败回调 错误捕获处理
                        try {
                            const failReason = failCallback(this.reason)
                            resolvePromise(promise2, failReason, resolve, reject)
                        } catch (error) {
                            reject(error)
                        }
                    }, 0)
                })
            }
        })
        return promise2
    }
}
function resolvePromise(promise2, resValue, resolve, reject) {
    if (resValue === promise2) {
        return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
    }
    if (resValue instanceof MyPromise) {
        resValue.then(value => resolve(value), reason => reject(reason))
    } else {
        resolve(resValue)
    }
}

// 验证
const mypromise =  new MyPromise((resolve, reject) => {
    // throw new Error('executor Error') // 执行器报错情形
    // resolve(100)
    // reject('失败')
    setTimeout(() => {
        resolve('成功')
    }, 1000)
})

mypromise.then(value => {
    console.log(value)
    return 'aaa'
    // throw new Error('resolve Err')
}, reason => {
    throw new Error('reject Err')
})
.then(value => {
    console.log(value)
}, reason => {
    console.log(reason)
})