Promise 和 async await

//Promise链式编程

function city() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('hunansheng')
            resolve('湖南')
        }, 300);
    })
}

function area(data) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('changshashi')
            resolve('长沙')
        }, 500);
    })
}

function list(data) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('yuhuaqu')
            resolve('雨花')
        }, 800);
    })
}
city().then(area).then(list).then((data) => {
    console.log(data)
})

// async 和  await
async function f1() {
    await fn()
    await fs()
}

function fn() {
    console.log("11")
}

function fs() {
    console.log("333")
}

f1()

// 分两次顺序执行
new Promise(resolve => {
    setTimeout(() => {
        resolve('hello')
    }, 2000)
}).then(val => {
    console.log(val) //  参数val = 'hello'
    return new Promise(resolve => {
        setTimeout(() => {
            resolve('world')
        }, 2000)
    })
}).then(val => {
    console.log(val) // 参数val = 'world'
})