async await promise demo

async await promise 实例

video demo

function step1(query) {
    return new Promise((success) => {
        let waiting=2000;
        setTimeout(() => {
           success('wait-time:'+waiting+' step:'+query);
        }, waiting);
    });
}
function step2(query) {
    return new Promise((success) => {
        let waiting=1000;
        setTimeout(() => {
            success('wait-time:'+waiting+' step:'+query);
        }, waiting);
    });
}
function step3(query) {
    return new Promise((success) => {
        let waiting=500;
        setTimeout(() => {
            success('wait-time:'+waiting+' step:'+query);
        }, waiting);
    });
}

const task = async()=>{
    await step1('step1').then((success) => {
        console.log(success);
    });

    await step2('step2').then((success) => {
        console.log(success);
    });

    await step3('step3').then(success => {
        console.log(success);
    });
};
task();
// step 1,2,3 setTimout'time is decrement,but will execute in order by async function tack