手写promise

// 手写一个promise
function pro (executor){
	let _this = this;
	_this.$$status = 'pending'
	_this.failCallback = undefined;
	_this.successCallback = undefined;
	_this.error = undefined ;
	setTimeout(_=>{
		executor(_this.resolve.bind(_this),_this.reject.bind(_this))
	})


}
	/**
	 *  promise 的 .then
	 *  .then 有两个参数，成功的回调函数及失败的回调
	 *  .then() .catch 都是返回了一个新的promise对象
	 */
	
	 /**
	  * promise 的链式调用
	  */
	pro.prototype.then = function(full,fail){
		let newPromi = new pro(_=>{})
		this.failCallback = fail;
		this.successCallback = full
		this.successDefer = newPromi.resolve.bind(newPromi)
		this.failDefer = newPromi.reject.bind(newPromi)
		return newPromi

	}

	pro.prototype.resolve = function (param){
		let _this = this;
		if (_this.$$status == 'pending'){
			_this.$$status = 'success'
			if (!_this.successCallback){
				return 
			}
			let result = _this.successCallback(param)
			if (result && result instanceof pro){
				result.then(_this.successDefer,_this.failDefer)
				return ''
			}
			_this.successDefer(result)
		}
	}

	pro.prototype.reject = function (){
		let _this = this;
		if (_this.$$status == 'pending'){
			_this.$$status = 'fail'
			if (_this.failCallback){
				return 
			}
			let result = _this.failCallback(param)
			if (result && result instanceof pro){
				result.then(_this.successDefer,_this.failDefer)
				return ''
			}
			_this.failDefer(failDefer)
		}
	}