在forEach循环中使用异步/等待

飞云Pro2020-03-13

在循环中使用async/ 是否有任何问题？我试图遍历文件数组和每个文件的内容。awaitforEachawait

import fs from 'fs-promise'

async function printFiles () {
  const files = await getFilePaths() // Assume this works fine

  files.forEach(async (file) => {
    const contents = await fs.readFile(file, 'utf8')
    console.log(contents)
  })
}

printFiles()

这段代码确实有效，但是这可能会出问题吗？我让某人告诉我，您不应该在这样的高阶函数中使用async/ await，所以我只是想问一下这是否有问题。

小宇宙Pro2020/03/13 17:55:15

只是添加到原始答案

原始答案中的并行读取语法有时会令人困惑且难以阅读，也许我们可以用其他方法编写它

async function printFiles() {
  const files = await getFilePaths();
  const fileReadPromises = [];

  const readAndLogFile = async filePath => {
    const contents = await fs.readFile(file, "utf8");
    console.log(contents);
    return contents;
  };

  files.forEach(file => {
    fileReadPromises.push(readAndLogFile(file));
  });

  await Promise.all(fileReadPromises);
}

对于顺序操作，不仅仅是for ... of，正常的for循环也将起作用

async function printFiles() {
  const files = await getFilePaths();

  for (let i = 0; i < files.length; i++) {
    const file = files[i];
    const contents = await fs.readFile(file, "utf8");
    console.log(contents);
  }
}

番长猴子古一2020/03/13 17:55:15

这是一些forEachAsync原型。请注意，您将需要await它们：

Array.prototype.forEachAsync = async function (fn) {
    for (let t of this) { await fn(t) }
}

Array.prototype.forEachAsyncParallel = async function (fn) {
    await Promise.all(this.map(fn));
}

Note while you may include this in your own code, you should not include this in libraries you distribute to others (to avoid polluting their globals).

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