Nodejs新特性async和await的使用详解_node.js_

if (true) { let a = 123; } console.log(a); // a is not defined

const PI = 3.1415926; PI = 3.15 // Assignment to constant variable. console.log(PI) 

setTimeout(() => { console.log("我被执行了") }, 1000) 

const name = "王五" var person = { // "name": name // name: name name } console.log(person.name) 

var name = "候七" var app = { name, // run: function(){ // console.log(`${this.name}在跑步`) // }, run(){ console.log(`${name}在跑步`) } } app.run() 

const name = "张三" const age = 27 console.log(`${name}的年龄是${age}`) 

function getData(){ // 异步 setTimeout(function(){ let name = "孙悟空"; return name }, 1000) } console.log(getData()) // undefined 

function getData(callback){ setTimeout(function(){ let name = "孙悟空"; callback(name); }, 1000) } getData(function(result){ console.log(result) // 孙悟空 }) 

var p = new Promise(function(resolve, reject){ setTimeout(function(){ let name = "猪八戒"; resolve(name) }, 1000); }) p.then(function(data){ console.log(data); }) 

async function test(){ // 通常异步方法中返回一个Promise对象，如果给定的是字符串，内部也会将其转换为Promise对象 return "hello nodejs"; } console.log(test()) // Promise {[[PromiseState]]: 'fulfilled', [[PromiseResult]]: 'hello nodejs', Symbol(async_id_symbol): 5, Symbol(trigger_async_id_symbol): 1} 

async function test(){ return new Promise(function(resolve, reject){ resolve("hello nodejs") }) } console.log(test()) 

async function test(){ return new Promise(function(resolve, reject){ resolve("hello nodejs") }) } // console.log(await test()) 错误写法 async function main(){ let result = await test(); // await必须用在async方法中 console.log(result) } main();