并行调用 async/await 函数

您可以等待：Promise.all()

await Promise.all([someCall(), anotherCall()]);

要存储结果，请执行以下操作：

let [someResult, anotherResult] = await Promise.all([someCall(), anotherCall()]);

请注意，失败的速度很快，这意味着一旦提供给它的一个承诺被拒绝，那么整个事情就会被拒绝。Promise.all

const happy = (v, ms) => new Promise((resolve) => setTimeout(() => resolve(v), ms))
const sad = (v, ms) => new Promise((_, reject) => setTimeout(() => reject(v), ms))

Promise.all([happy('happy', 100), sad('sad', 50)])
  .then(console.log).catch(console.log) // 'sad'

相反，如果您想等待所有承诺履行或拒绝，则可以使用 Promise.allSettled。请注意，Internet Explorer 本身不支持此方法。

const happy = (v, ms) => new Promise((resolve) => setTimeout(() => resolve(v), ms))
const sad = (v, ms) => new Promise((_, reject) => setTimeout(() => reject(v), ms))

Promise.allSettled([happy('happy', 100), sad('sad', 50)])
  .then(console.log) // [{ "status":"fulfilled", "value":"happy" }, { "status":"rejected", "reason":"sad" }]

注意：如果您使用的操作在拒绝发生之前设法完成，则不会回滚，因此您可能需要处理这种情况。例如 如果您有 5 个操作，则 4 个快速、1 个慢速和慢速拒绝。那 4 操作可能已执行，因此可能需要回滚。在这种情况下，请考虑使用 while 它将提供哪些操作失败和哪些操作失败的确切详细信息。Promise.allPromise.allSettled

TL;博士

用于并行函数调用时，发生错误时应答行为不正确。Promise.all

首先，一次执行所有异步调用并获取所有对象。其次，在物体上使用。这样，当您等待第一个问题解决时，其他异步调用仍在进行中。总体而言，您只会等待最慢的异步调用。例如：PromiseawaitPromisePromise

// Begin first call and store promise without waiting
const someResult = someCall();

// Begin second call and store promise without waiting
const anotherResult = anotherCall();

// Now we await for both results, whose async processes have already been started
const finalResult = [await someResult, await anotherResult];

// At this point all calls have been resolved
// Now when accessing someResult| anotherResult,
// you will have a value instead of a promise

JSbin 示例：http://jsbin.com/xerifanima/edit?js,console

警告：无论调用是在同一条线路上还是在不同线路上，只要第一次调用发生在所有异步调用之后即可。请参阅 JohnnyHK 的评论。awaitawait

更新：根据@bergi的答案，此答案在错误处理中具有不同的时间，它不会在错误发生时抛出错误，而是在所有承诺执行之后抛出错误。 我将结果与@jonny的提示进行比较： ，检查以下代码片段[result1, result2] = Promise.all([async1(), async2()])

const correctAsync500ms = () => {
  return new Promise(resolve => {
    setTimeout(resolve, 500, 'correct500msResult');
  });
};

const correctAsync100ms = () => {
  return new Promise(resolve => {
    setTimeout(resolve, 100, 'correct100msResult');
  });
};

const rejectAsync100ms = () => {
  return new Promise((resolve, reject) => {
    setTimeout(reject, 100, 'reject100msError');
  });
};

const asyncInArray = async (fun1, fun2) => {
  const label = 'test async functions in array';
  try {
    console.time(label);
    const p1 = fun1();
    const p2 = fun2();
    const result = [await p1, await p2];
    console.timeEnd(label);
  } catch (e) {
    console.error('error is', e);
    console.timeEnd(label);
  }
};

const asyncInPromiseAll = async (fun1, fun2) => {
  const label = 'test async functions with Promise.all';
  try {
    console.time(label);
    let [value1, value2] = await Promise.all([fun1(), fun2()]);
    console.timeEnd(label);
  } catch (e) {
    console.error('error is', e);
    console.timeEnd(label);
  }
};

(async () => {
  console.group('async functions without error');
  console.log('async functions without error: start')
  await asyncInArray(correctAsync500ms, correctAsync100ms);
  await asyncInPromiseAll(correctAsync500ms, correctAsync100ms);
  console.groupEnd();

  console.group('async functions with error');
  console.log('async functions with error: start')
  await asyncInArray(correctAsync500ms, rejectAsync100ms);
  await asyncInPromiseAll(correctAsync500ms, rejectAsync100ms);
  console.groupEnd();
})();

我投票给：

await Promise.all([someCall(), anotherCall()]);

请注意，在调用函数的那一刻，可能会导致意外结果：

// Supposing anotherCall() will trigger a request to create a new User

if (callFirst) {
  await someCall();
} else {
  await Promise.all([someCall(), anotherCall()]); // --> create new User here
}

但以下总是会触发创建新用户的请求

// Supposing anotherCall() will trigger a request to create a new User

const someResult = someCall();
const anotherResult = anotherCall(); // ->> This always creates new User

if (callFirst) {
  await someCall();
} else {
  const finalResult = [await someResult, await anotherResult]
}

更新：

原始答案使得正确处理承诺拒绝变得困难（在某些情况下是不可能的）。正确的解决方案是使用：Promise.all

const [someResult, anotherResult] = await Promise.all([someCall(), anotherCall()]);

原答案：

只需确保在等待任何一个函数之前调用这两个函数：

// Call both functions
const somePromise = someCall();
const anotherPromise = anotherCall();

// Await both promises    
const someResult = await somePromise;
const anotherResult = await anotherPromise;

我创建了一个辅助函数 waitAll，也许它可以让它更甜蜜。 它目前仅适用于 nodejs，不适用于浏览器 chrome。

    //const parallel = async (...items) => {
    const waitAll = async (...items) => {
        //this function does start execution the functions
        //the execution has been started before running this code here
        //instead it collects of the result of execution of the functions

        const temp = [];
        for (const item of items) {
            //this is not
            //temp.push(await item())
            //it does wait for the result in series (not in parallel), but
            //it doesn't affect the parallel execution of those functions
            //because they haven started earlier
            temp.push(await item);
        }
        return temp;
    };

    //the async functions are executed in parallel before passed
    //in the waitAll function

    //const finalResult = await waitAll(someResult(), anotherResult());
    //const finalResult = await parallel(someResult(), anotherResult());
    //or
    const [result1, result2] = await waitAll(someResult(), anotherResult());
    //const [result1, result2] = await parallel(someResult(), anotherResult());

我创建了一个要点，测试一些不同的解决承诺的方法，并取得了结果。查看有效的选项可能会有所帮助。

编辑：根据 Jin Lee 的评论的要点内容

// Simple gist to test parallel promise resolution when using async / await

function promiseWait(time) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(true);
    }, time);
});
}


async function test() {
    return [
    await promiseWait(1000),
    await promiseWait(5000),
    await promiseWait(9000),
    await promiseWait(3000),
    ]
}

async function test2() {
    return {
        'aa': await promiseWait(1000),
        'bb': await promiseWait(5000),
        'cc': await promiseWait(9000),
        'dd': await promiseWait(3000),
    }
}

async function test3() {
    return await {
        'aa': promiseWait(1000),
        'bb': promiseWait(5000),
        'cc': promiseWait(9000),
        'dd': promiseWait(3000),
    }
}

async function test4() {
    const p1 =  promiseWait(1000);
    const p2 =  promiseWait(5000);
    const p3 =  promiseWait(9000);
    const p4 =  promiseWait(3000);
    return {
        'aa': await p1,
        'bb': await p2,
        'cc': await p3,
        'dd': await p4,
    };
}

async function test5() {
    return await Promise.all([
                             await promiseWait(1000),
                             await promiseWait(5000),
                             await promiseWait(9000),
                             await promiseWait(3000),
                             ]);
}

async function test6() {
    return await Promise.all([
                             promiseWait(1000),
                             promiseWait(5000),
                             promiseWait(9000),
                             promiseWait(3000),
                             ]);
}

async function test7() {
    const p1 =  promiseWait(1000);
    const p2 =  promiseWait(5000);
    const p3 =  promiseWait(9000);
    return {
        'aa': await p1,
        'bb': await p2,
        'cc': await p3,
        'dd': await promiseWait(3000),
    };
}

let start = Date.now();

test().then((res) => {
    console.log('Test Done, elapsed', (Date.now() - start) / 1000, res);

    start = Date.now();
    test2().then((res) => {
        console.log('Test2 Done, elapsed', (Date.now() - start) / 1000, res);

        start = Date.now();
        test3().then((res) => {
            console.log('Test3 Done, elapsed', (Date.now() - start) / 1000, res);

            start = Date.now();
            test4().then((res) => {
                console.log('Test4 Done, elapsed', (Date.now() - start) / 1000, res);

                start = Date.now();
                test5().then((res) => {
                    console.log('Test5 Done, elapsed', (Date.now() - start) / 1000, res);

                    start = Date.now();
                    test6().then((res) => {
                        console.log('Test6 Done, elapsed', (Date.now() - start) / 1000, res);
                    });

                    start = Date.now();
                    test7().then((res) => {
                        console.log('Test7 Done, elapsed', (Date.now() - start) / 1000, res);
                    });
                });
            });

        });
    });

});
/*
Test Done, elapsed 18.006 [ true, true, true, true ]
Test2 Done, elapsed 18.009 { aa: true, bb: true, cc: true, dd: true }
Test3 Done, elapsed 0 { aa: Promise { <pending> },
  bb: Promise { <pending> },
  cc: Promise { <pending> },
  dd: Promise { <pending> } }
Test4 Done, elapsed 9 { aa: true, bb: true, cc: true, dd: true }
Test5 Done, elapsed 18.008 [ true, true, true, true ]
Test6 Done, elapsed 9.003 [ true, true, true, true ]
Test7 Done, elapsed 12.007 { aa: true, bb: true, cc: true, dd: true }
*/

还有另一种方法可以在没有 Promise.all（） 的情况下并行执行此操作：

首先，我们有 2 个函数来打印数字：

function printNumber1() {
   return new Promise((resolve,reject) => {
      setTimeout(() => {
      console.log("Number1 is done");
      resolve(10);
      },1000);
   });
}

function printNumber2() {
   return new Promise((resolve,reject) => {
      setTimeout(() => {
      console.log("Number2 is done");
      resolve(20);
      },500);
   });
}

这是连续的：

async function oneByOne() {
   const number1 = await printNumber1();
   const number2 = await printNumber2();
} 
//Output: Number1 is done, Number2 is done

这是并行的：

async function inParallel() {
   const promise1 = printNumber1();
   const promise2 = printNumber2();
   const number1 = await promise1;
   const number2 = await promise2;
}
//Output: Number2 is done, Number1 is done

    // A generic test function that can be configured 
    // with an arbitrary delay and to either resolve or reject
    const test = (delay, resolveSuccessfully) => new Promise((resolve, reject) => setTimeout(() => {
        console.log(`Done ${ delay }`);
        resolveSuccessfully ? resolve(`Resolved ${ delay }`) : reject(`Reject ${ delay }`)
    }, delay));

    // Our async handler function
    const handler = async () => {
        // Promise 1 runs first, but resolves last
        const p1 = test(10000, true);
        // Promise 2 run second, and also resolves
        const p2 = test(5000, true);
        // Promise 3 runs last, but completes first (with a rejection) 
        // Note the catch to trap the error immediately
        const p3 = test(1000, false).catch(e => console.log(e));
        // Await all in parallel
        const r = await Promise.all([p1, p2, p3]);
        // Display the results
        console.log(r);
    };

    // Run the handler
    handler();
    /*
    Done 1000
    Reject 1000
    Done 5000
    Done 10000
    */

虽然设置 p1、p2 和 p3 并不是严格地并行运行它们，但它们不会阻碍任何执行，并且您可以使用捕获来捕获上下文错误。

就我而言，我有几个任务要并行执行，但我需要对这些任务的结果做一些不同的事情。

function wait(ms, data) {
    console.log('Starting task:', data, ms);
    return new Promise(resolve => setTimeout(resolve, ms, data));
}

var tasks = [
    async () => {
        var result = await wait(1000, 'moose');
        // do something with result
        console.log(result);
    },
    async () => {
        var result = await wait(500, 'taco');
        // do something with result
        console.log(result);
    },
    async () => {
        var result = await wait(5000, 'burp');
        // do something with result
        console.log(result);
    }
]

await Promise.all(tasks.map(p => p()));
console.log('done');

输出：

Starting task: moose 1000
Starting task: taco 500
Starting task: burp 5000
taco
moose
burp
done

(async function(){
function wait(ms, data) {
    console.log('Starting task:', data, ms);
    return new Promise(resolve => setTimeout(resolve, ms, data));
}

var tasks = [
    async () => {
        var result = await wait(1000, 'moose');
        // do something with result
        console.log(result);
    },
    async () => {
        var result = await wait(500, 'taco');
        // do something with result
        console.log(result);
    },
    async () => {
        var result = await wait(5000, 'burp');
        // do something with result
        console.log(result);
    }
]

await Promise.all(tasks.map(p => p()));
console.log('done');
})();

等待 Promise.all（[someCall（）， anotherCall（）]）;如前所述，它将充当线程围栏（在 CUDA 并行代码中非常常见），因此它将允许其中的所有承诺在不阻塞彼此的情况下运行，但会阻止执行继续，直到 ALL 得到解决。

另一种值得分享的方法是 Node.js 异步，它还允许您轻松控制通常需要的并发量，如果任务直接链接到 API 调用、I/O 操作等有限资源的使用。

// create a queue object with concurrency 2
var q = async.queue(function(task, callback) {
  console.log('Hello ' + task.name);
  callback();
}, 2);

// assign a callback
q.drain = function() {
  console.log('All items have been processed');
};

// add some items to the queue
q.push({name: 'foo'}, function(err) {
  console.log('Finished processing foo');
});

q.push({name: 'bar'}, function (err) {
  console.log('Finished processing bar');
});

// add some items to the queue (batch-wise)
q.push([{name: 'baz'},{name: 'bay'},{name: 'bax'}], function(err) {
  console.log('Finished processing item');
});

// add some items to the front of the queue
q.unshift({name: 'bar'}, function (err) {
  console.log('Finished processing bar');
});

感谢 Medium 文章 autor （阅读更多)

您可以调用多个异步函数，而无需等待它们。这将并行执行它们。在执行此操作时，将返回的 promise 保存在变量中，并在某个时间点单独或使用 Promise.all（） 等待它们并处理结果。

您还可以使用 try 包装函数调用...catch 用于处理单个异步操作的失败并提供回退逻辑。

下面是一个示例： 观察日志，在各个异步函数执行开始时打印的日志会立即打印出来，即使第一个函数需要 5 秒才能解决。

function someLongFunc () {
    return new Promise((resolve, reject)=> {
        console.log('Executing function 1')
        setTimeout(resolve, 5000)
    })
}

function anotherLongFunc () {
    return new Promise((resolve, reject)=> {
        console.log('Executing function 2')
        setTimeout(resolve, 5000)
    })
}

async function main () {
    let someLongFuncPromise, anotherLongFuncPromise
    const start = Date.now()
    try {
        someLongFuncPromise = someLongFunc()
    }
    catch (ex) {
        console.error('something went wrong during func 1')
    }

    try {
        anotherLongFuncPromise = anotherLongFunc()
    }
    catch (ex) {
        console.error('something went wrong during func 2')
    }

    await someLongFuncPromise
    await anotherLongFuncPromise
    const totalTime = Date.now() - start
    console.log('Execution completed in ', totalTime)
}

main()

这可以通过 Promise.allSettled（） 来实现，它类似于 Promise.all（），但没有快速失败行为。

async function Promise1() {
    throw "Failure!";
}

async function Promise2() {
    return "Success!";
}

const [Promise1Result, Promise2Result] = await Promise.allSettled([Promise1(), Promise2()]);

console.log(Promise1Result); // {status: "rejected", reason: "Failure!"}
console.log(Promise2Result); // {status: "fulfilled", value: "Success!"}

注意：这是一个前沿功能，浏览器支持有限，因此我强烈建议为此功能添加 polyfill。