JS Promise

var pa1 = function () {
	console.log('爬一楼');
 
	return {
		success: (fun) => {fun();}
	}
};
 
var pa2 = function () {
	console.log('爬二楼');
 
 
	return {success: (fun) => {fun();}}
};
var pa3 = function () {
	console.log('爬三楼');
 
 
	return {
		success: function () {
    	    
		}
	}
};
 
function promiseAaa (i) {
	return new Promise(function(resolve, reject) {
		let k = 1;
 
    	function _fun(k) {
			k++;
			console.log('downloading', k);
 
			if (k > 10) {
				console.log('download ok!');
            	return resolve();
// 				return reject();
			}
 
			_fun(k);
		}
		
		_fun(k);
	});
}
 
promiseAaa().then(function () {
	console.log('download finish');
})

Promise应用场景：比如下载东西

一定要做完一件事，再做下一件事情，爬楼梯，你一定要成功爬了1楼才能爬2楼，然后3楼，跟嵌套函数略有区别，promise是链式写法，可以写成一行。而嵌套函数不能写成一行，空格会很多。

 

还有个简单的?，比上面的简单易懂多了

 

new Promise(function(resolve, reject) {

     setTimeout(function(){ resolve(1); }, 1000);

})

.then(function(number) { console.log('number1', number); return number + 1; })

.then(function(number) { console.log('number2', number); return number + 1; })

.then(function(number) { console.log('number3 ',number);});




//  number1 1
//  number2 2
//  number3 3

原博客地址! https://blog.youkuaiyun.com/ghostyusheng/article/details/84001214