Pormise

function MyPromise (executor) {
    var self = this
    self.status = 'pending'
    self.resolveValue = null
    self.rejectValue = null
    self.resolveCallbackList = []
    self.rejectCallbackList = []

    function resolve (value) {
        if (self.status === 'pending') {
            self.status = 'Fulfilled'
            self.resolveValue = value
            self.resolveCallbackList.forEach(function (item) {
                item()
            })
        }

    }

    function reject (value) {
        if(self.status === 'pending') {
            self.status = 'Rejected'
            self.rejectValue = value
            self.rejectCallbackList.forEach(function (item) {
                item()
            })
        }
    }
    try {
        executor(resolve, reject)
    } catch (e) {
        reject(e)
    }
}
    function resultIsPromise (nextValue, res, rej) {
        if(nextValue instanceof MyPromise) {
            nextValue.then(function (val) {
                res(val)
            }, function(reason) {
                rej(reason)
            })
        } else {
            res(nextValue)
        }
    }
    MyPromise.prototype.then = function (resolve, reject) {
        if (!resolve) {
             resolve = function(val) {
                return val
            }
        }
        if (!reject) {
             reject = function (val) {
                throw new Error(val)
            }
        }
        var self = this
        var nextPromise = new MyPromise(function(res, rej) {
                setTimeout(function() {
                    if (self.status === 'Fulfilled') {
                    try{
                        // var newResolveVal = resolve(self.resolveValue)
                        // res(newResolveVal)
                        var newResolveVal = resolve(self.resolveValue)
                        resultIsPromise(newResolveVal, res, rej)
                    } catch(e) {
                        rej(e)
                        }
                    }
                }, 0)

                setTimeout(function () {
                    if (self.status === 'Rejected') {
                    try{
                        var newRejectVal = reject(self.rejectValue)
                        resultIsPromise(newRejectVal, res, rej)
                    } catch(e) {
                        rej(e)
                    }
                    }
                }, 0)

            if (self.status === 'pending') {
                if(typeof resolve === 'function') {
                    self.resolveCallbackList.push(function () {
                        setTimeout(function() {
                            try{
                                var newResolveVal = resolve(self.resolveValue)
                                resultIsPromise(newResolveVal, res, rej)
                            } catch (e) {
                                rej(e)
                            }
                        })
                    })
                }
                if(typeof reject === 'function') {
                    setTimeout(function () {
                        self.rejectCallbackList.push(function () {
                            try{
                                var newRejectVal = reject(self.rejectValue)
                                resultIsPromise(newRejectVal, res, rej)
                            } catch(e) {
                              rej(e)
                            }
                        })
                    }, 0)
                }
            }
        })
        return nextPromise
}