promise6.js

// 添加拒绝方法，添加一个数组方法存放

function Promise(fn) {
    var promise = this;
        promise._value;
        promise._reason;
        promise._resolves = [];
        promise._rejects = [];
        promise._status = 'PENDING';

    this.then = function (onFulfilled, onRejected) {
        return new Promise(function(resolve, reject) {
            function handle(value) {
                var ret = typeof onFulfilled === 'function' && onFulfilled(value) || value;
                if(ret && typeof ret ['then'] == 'function'){
                    ret.then(function(value){
                       resolve(value);
                    },function(reason){
                       reject(reason);
                    });
                } else {
                    resolve(ret);
                }
            }
            function errback(reason){
                reason = typeof onRejected === 'function' && onRejected(reason) || reason;
                reject(reason);
            }
            if (promise._status === 'PENDING') {
                promise._resolves.push(handle);
                promise._rejects.push(errback);
            } else if(promise._status === 'FULFILLED'){
                handle(promise._value);
            } else if(promise._status === 'REJECTED') {
            errback(promise._reason);
        }
        })
        
    };


    function resolve(value) {
        setTimeout(function(){
            promise._status = "FULFILLED";
            promise._resolves.forEach(function (callback) {
                value = callback( value);
            })
        },0);
    }

    function reject(value) {
        setTimeout(function(){
            promise._status = "REJECTED";
            promise._rejects.forEach(function (callback) {
                promise._reason = callback(value);
            })
        },0);
    }

    fn(resolve, reject);
}