async demo

async.ts

async function sleep(name: string, ms: number) {
    await new Promise(resolve => {
        console.log(`${name} sleep ${ms} seconds`);
        setTimeout(resolve, ms);
    });
}

async function forEachLoop() {
    const numbers = [1, 2, 3, 4, 5];
    const basetime = Date.now();
    numbers.forEach(async n => {
        console.log('forEach in: ', n, 'elapse time: ', Date.now() - basetime);
        await sleep(`forEach ${n}`, Math.floor(2000 + Math.random() * 1000));
        console.log('forEach out: ', n, 'elapse time: ', Date.now() - basetime);
    });
}

async function forOfLoop() {
    const numbers = [1, 2, 3, 4, 5];
    const basetime = Date.now();
    for (const n of numbers) {
        console.log('forOf in: ', n, 'elapse time: ', Date.now() - basetime);
        await sleep(`forOf ${n}`, Math.floor(2000 + Math.random() * 1000));
        console.log('forOf out: ', n, 'elapse time: ', Date.now() - basetime);
    }
}

async function main() {
    console.time('不使用 await');
    sleep(`no await`, 5000);
    console.timeEnd('不使用 await');

    console.log('\n');

    console.time('使用 await');
    await sleep(`use await`, 5000);
    console.timeEnd('使用 await');

    console.log('\n');

    console.log('使用 forEach，不会按序执行，注意查看 forEach out 是乱序的');
    forEachLoop();

    console.log('\n');

    console.log('使用 forOf，会按序执行，注意查看 forOf in 和 forOf out 一一对应');
    forOfLoop();
}

main();