File Handling Programs

Node.js file programs should handle explicit paths, file encodings, I/O failures, and cleanup. fs/promises offers asynchronous operations with Promise return types. Use a temporary directory in demos so running the lesson does not overwrite a student's real files.

The program creates a new temporary folder, writes a UTF-8 file, reads the exact contents, and removes the folder inside finally even if an operation throws.

Don't silently replace arbitrary paths or ignore write failures; filesystem operations need error handling and permissions.

This source was compiled using TypeScript 5.8.3 with strict checking, then executed with Node.js 22.16.0. Its stdout below is the actual captured output. The core logic is runnable without a framework or a remote API; integration-specific examples appear in a separate lab when needed.

TypeScript source

import { mkdtemp, writeFile, readFile, rm } from "node:fs/promises";
import { tmpdir } from "node:os";
import { join } from "node:path";
async function main(): Promise<void> {
  const dir = await mkdtemp(join(tmpdir(), "ts-example-"));
  try {
    const file = join(dir, "note.txt");
    await writeFile(file, "Read TypeScript", "utf8");
    console.log(await readFile(file, "utf8"));
  } finally { await rm(dir, { recursive: true, force: true }); }
}
main().catch(console.error);

Verified output

Read TypeScript

Compile: npx tsc --strict --target es2022 --module commonjs file-handling-programs.ts; run: node file-handling-programs.js. For examples importing node: modules, install @types/node as a development dependency; for browser or React projects use the separate lab setup.

The program creates a new temporary folder, writes a UTF-8 file, reads the exact contents, and removes the folder inside finally even if an operation throws.

Before editing the code, predict what the output will be for one changed input. Run it and compare your prediction with the actual result.

Don't silently replace arbitrary paths or ignore write failures; filesystem operations need error handling and permissions.

Determine whether the issue belongs to the type system, a trust boundary, or actual runtime behavior before choosing a correction.

Save two temporary files and report their combined byte size using stat.

Record expected success and failure outcomes, run the code, and compare the observed behavior. Keep the exercise compatible with strict type checking.

The program creates a new temporary folder, writes a UTF-8 file, reads the exact contents, and removes the folder inside finally even if an operation throws.

Apply the same reasoning to the practice task, then integrate it into a real app only when the runtime and dependency setup are ready.