TypeScript 函数中 Promise 返回值类型

Question

export function fsReadDir(dir:string) { // Promise<unknown>
// export function fsReadDir(dir:string): Promise<Dirent[]> {
    return new Promise((resolve, reject) => {
      fs.readdir(dir, { withFileTypes: true }, (err: any, files: Dirent[]) => {
        if (err) {
          console.log(err);
          reject(err);
        }
        resolve(files);
      });
    }).catch(reason=>{
      // dosome
    });
  }

我想让 函数返回值带有 Promise<Dirent[]>

Answer 1

直接修改原码

给 Promise 加类型参数，注意 catch 返回的东西其实也是 resolve，所以返回一个空数组。

import type { Dirent } from "fs";
import fs from "fs";

export function fsReadDir(dir: string): Promise<Dirent[]> { // Promise<unknown>
    // export function fsReadDir(dir:string): Promise<Dirent[]> {
    return new Promise<Dirent[]>((resolve, reject) => {
        fs.readdir(dir, { withFileTypes: true }, (err: any, files: Dirent[]) => {
            if (err) {
                console.log(err);
                reject(err);
            }
            resolve(files);
        });
    }).catch(reason => {
        // dosome
        return [] as Dirent[];
    });
}

如果 Node 版本较新

fs 提供了 promises 接口，版本历史

Version	Changes
v14.0.0	Exposed as require('fs/promises').
v11.14.0, v10.17.0	This API is no longer experimental.
v10.1.0	The API is accessible via require('fs').promises only.
v10.0.0	Added in: v10.0.0

import type { Dirent } from "fs";
import fs from "fs";
const fsPromise = fs.promises;

export function fsReadDir(dir: string): Promise<Dirent[]> {
    return fsPromise.readdir(dir, { withFileTypes: true });
}

如果要处理错误

export function fsReadDir(dir: string): Promise<Dirent[]> {
    return fsPromise
        .readdir(dir, { withFileTypes: true })
        .catch(err => []);
}

再补充个 await 的写法（其实前面两段都可以加 async 修饰，不过返回的反正都是 Promise，加不加都无所谓）

export async function fsReadDir(dir: string): Promise<Dirent[]> {
    try {
        return await fsPromise.readdir(dir, { withFileTypes: true })
    } catch (err: unknown) {
        console.log(err);
        return [];
    }
}