node.js async/await 繼發執行與併發執行

async/await 繼發執行與併發執行，看如何控制

兩個異步函數 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)
    })
}

繼發執行

//繼發執行
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())
}


//繼發執行
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())
}

併發執行

//併發執行 
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())
}


//併發執行 
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())

}


//併發執行
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())
}

//併發執行 可是 會先執行 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())
}