概述

Promise: 解决callback嵌套问题， .then()等promise fulfilled后触发， .then()和.catch()可以嵌套
await 等待Promise fulfilled，返回其结果，或者抛出异常
async: 将一个普通方法转换成返回Promise

示例

function deferedSayHello(){
	return new Promise(function(resolve, reject){
		setTimeout(function(){
			resolve("javacoder.cn")
		},2000);
	});
}

//Async 关键字将函数的返回值封装成Promise对象
async function hello() {
	console.log("befor deferedSayHello");
	// 直接调用异步函数返回的是Pending状态的Promise
	console.log(deferedSayHello())
	//await 等待Promise fulfilled, 返回的是结果或者异常
	console.log(await deferedSayHello())
	console.log("after deferedSayHello");
}
hello()

function deferedSayHello(){

return new Promise(function(resolve, reject){

setTimeout(function(){

resolve("javacoder.cn")

},2000);

});

}

//Async 关键字将函数的返回值封装成Promise对象

async function hello() {

console.log("befor deferedSayHello");

// 直接调用异步函数返回的是Pending状态的Promise

console.log(deferedSayHello())

//await 等待Promise fulfilled, 返回的是结果或者异常

console.log(await deferedSayHello())

console.log("after deferedSayHello");

}

hello()

输出

befor deferedSayHello
Promise {<pending>}
javacoder.cn
after deferedSayHello

Posted in: IT人生

知行合一，止于至善

javascript Promise async await

概述

示例

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