Node.js & file system & async await & forEach bug All In One

Async / Await & Top-level await

await & `forEach` bug ❌

const fs = require("fs").promises;
const path = require("path");

// const items = await fs.readdir("stores");
// console.log(items);

// SyntaxError: await is only valid in async functions and the top level bodies of modules
async function main() {
  // const items = await fs.readdir("stores", { withFileTypes: true });
  // for (let item of items) {
  //   const type = item.isDirectory() ? "folder" : "file";
  //   console.log(`${item.name}: ${type}`);
  // }

  async function findFiles(folderName, arr = []) {
    let result = arr ?? [];
    // 'await' expressions are only allowed within async functions and at the top levels of modules.ts(1308)
    const items = await fs.readdir(folderName, { withFileTypes: true });
    // ❌ items.forEach 使用 async function 包裹后，导致 await 层级 bug
    items.forEach(async (item) => {
      if (path.extname(item.name) === ".json") {
        console.log(`Found file: ${item.name} in folder: ${folderName}`);
        // result.push(`${folderName}${item.name}`);
        result.push(path.join(folderName, item.name));
      } else {
        // this is a folder, so call this method again and pass in
        // the path to the folder
        await findFiles(path.join(folderName, item.name), result);
      }
    });
    return result;
  }

  const files = await findFiles("stores");
  console.log(`✅ files =`, files);
}

main();

solution

for...of

const fs = require("fs").promises;
const path = require("path");

// const items = await fs.readdir("stores");
// console.log(items); 

// SyntaxError: await is only valid in async functions and the top level bodies of modules
async function main() {
  // const items = await fs.readdir("stores", { withFileTypes: true });
  // for (let item of items) {
  //   const type = item.isDirectory() ? "folder" : "file";
  //   console.log(`${item.name}: ${type}`);
  // }

  async function findFiles(folderName, arr = []) {
    let result = arr ?? [];
    // 'await' expressions are only allowed within async functions and at the top levels of modules.ts(1308)
    const items = await fs.readdir(folderName, { withFileTypes: true });
    // ❌ items.forEach 使用 async function 包裹后，导致 await 层级 bug
    // items.forEach(async (item) => {
    //   if (path.extname(item.name) === ".json") {
    //     console.log(`Found file: ${item.name} in folder: ${folderName}`);
    //     // result.push(`${folderName}${item.name}`);
    //     result.push(path.join(folderName, item.name));
    //   } else {
    //     // this is a folder, so call this method again and pass in
    //     // the path to the folder
    //     await findFiles(path.join(folderName, item.name), result);
    //   }
    // });
    // for...of ✅ 不需要使用一层 async function 包裹
    for (const item of items) {
      if (path.extname(item.name) === ".json") {
        // console.log(`Found file: ${item.name} in folder: ${folderName}`);
        // result.push(`${folderName}${item.name}`);
        result.push(path.join(folderName, item.name));
      } else {
        // this is a folder, so call this method again and pass in
        // the path to the folder
        await findFiles(path.join(folderName, item.name), result);
      }
    }
    return result;
  }

  const files = await findFiles("stores");
  console.log(`✅ files =`, files);
}

main();