异步请求

function ajaxOne() {
    return new Promise((resolve, reject) => {
        setTimeout(function () {
            resolve('ajaxOne loaded!')
        }, 1000)
    })
}
function ajaxTwo() {
    return new Promise((resolve, reject) => {
        setTimeout(function () {
            resolve('ajaxTwo loaded!')
        }, 2000)
    })
}
...

等待异步请求结束

asycn function runAsync() {
    await ajaxOne()
    await ajaxTwo()
    // 上面的异步请求完成后才会往下执行
    console.log('do sometion')
}

runAsync().then(() => {
    console.log('do sometion')
})