no-await-in-loop

禁止循环内的 await

对可迭代的每个元素执行操作是一项常见任务。但是，在每个操作中执行 await 表明程序没有充分利用 async/await 的并行化优势。

通常，应该重构代码以一次创建所有 Promise，然后使用 Promise.all() 访问结果。否则，每个后续操作将在前一个操作完成之前不会开始。

具体来说，应该重构以下函数，如下所示：

async function foo(things) {
  const results = [];
  for (const thing of things) {
    // Bad: each loop iteration is delayed until the entire asynchronous operation completes
    results.push(await bar(thing));
  }
  return baz(results);
}

async function foo(things) {
  const results = [];
  for (const thing of things) {
    // Good: all asynchronous operations are immediately started.
    results.push(bar(thing));
  }
  // Now that all the asynchronous operations are running, here we wait until they all complete.
  return baz(await Promise.all(results));
}

规则详情

该规则不允许在循环体中使用 await。

示例

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/*eslint no-await-in-loop: "error"*/

async function foo(things) {
  const results = [];
  for (const thing of things) {
    // Good: all asynchronous operations are immediately started.
    results.push(bar(thing));
  }
  // Now that all the asynchronous operations are running, here we wait until they all complete.
  return baz(await Promise.all(results));
}

P6820Z8G9wSG50SW7a53cABVQLzOImcIRV+hQUkxjXCO67pG2wyQwHch0OYzHhMo

/*eslint no-await-in-loop: "error"*/

async function foo(things) {
  const results = [];
  for (const thing of things) {
    // Bad: each loop iteration is delayed until the entire asynchronous operation completes
    results.push(await bar(thing));
  }
  return baz(results);
}

何时不使用

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