async await 链式同步处理异步

function doubleAfter2seconds(num,data) {

    return new Promise((resolve) => {

        setTimeout(() => {

            resolve(2 * num)

        }, data);

    } )

}

async function testResult() {

  console.log('开始')

    let first = await doubleAfter2seconds(10,2000)

    first+=100

    console.log(first)

    let second = await doubleAfter2seconds(first+1,1000);

    let third = await doubleAfter2seconds(second+1,200);

    console.log(first);

    console.log(second);

    console.log(third);

    console.log('结束')

}