Nodejs新特性async和await的使用详解

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();