node.js async/await 继发执行与并发执行

async/await 继发执行与并发执行，看如何控制

两个异步函数 foo bar

function foo() {

    return new Promise((resolve, reject) => {

        setTimeout(() => {

            console.log('foo:' + new Date().toLocaleString())

            resolve('foo')

        }, 2000)

    })

}

function bar() {

    return new Promise((resolve, reject) => {

        setTimeout(() => {

            console.log('bar:' + new Date().toLocaleString())

            resolve('bar')

        }, 2000)

    })

}

继发执行

//继发执行

async function main() {

    console.log('beginTime:' + new Date().toLocaleString())

    var foostr = await foo();

    console.log(new Date().toLocaleString())

    console.log(foostr);

    var barstr = await bar();

    console.log(new Date().toLocaleString())

    console.log(barstr);

    console.log('endTime:' + new Date().toLocaleString())

}

//继发执行

async function main2() {

    let docs = [foo, bar];

    console.log('beginTime:' + new Date().toLocaleString())

    for (let doc of docs) {

        var str = await doc();

        console.log(new Date().toLocaleString())

        console.log(str);

    }

    console.log('endTime:' + new Date().toLocaleString())

}

并发执行

//并发执行

async function async_main() {

    console.log('beginTime:' + new Date().toLocaleString())

    let [get_foo, get_bar] = await Promise.all([foo(), bar()]);

    console.log(new Date().toLocaleString());

    console.log(get_foo);

    console.log(get_bar);

    console.log('endTime:' + new Date().toLocaleString())

}

//并发执行

async function async_main4() {

    let docs = [foo(), bar()];

    console.log('beginTime:' + new Date().toLocaleString())

    for (let doc of docs) {

        var str = await doc;

        console.log(new Date().toLocaleString())

        console.log(str);

    }

    console.log('endTime:' + new Date().toLocaleString())

}

//并发执行

async function async_main2() {

    console.log('beginTime:' + new Date().toLocaleString())

    let fooPromise = foo();

    let barPromise = bar();

    let get_foo = await fooPromise;

    console.log(new Date().toLocaleString());

    console.log(get_foo);

    let get_bar = await barPromise;

    console.log(new Date().toLocaleString());

    console.log(get_bar);

    console.log('endTime:' + new Date().toLocaleString())

}

//并发执行 但是 会先执行 endTime

async function async_main3() {

    let docs = [foo, bar];

    console.log('beginTime:' + new Date().toLocaleString())

    docs.forEach(async (val) => {

        var str = await val();

        console.log(new Date().toLocaleString())

        console.log(str);

    })

    console.log('endTime:' + new Date().toLocaleString())

}