Reading and Writing Files

The node:fs/promises API provides asynchronous filesystem operations such as readFile and writeFile. Pass encodings when you want text; otherwise a read returns bytes. Handle missing files and permissions errors and prefer a controlled path when writing application data.

mkdtemp creates a unique temporary directory; writeFile stores the text; readFile returns a string with utf8 encoding. The finally block removes created files, including if an operation fails.

Avoid writing to fixed shared paths in examples; temporary directories prevent overwriting a user's real files.

Save as reading-writing-files.ts. The following program passed strict TypeScript compilation, and the displayed output was captured by executing its emitted JavaScript with Node.js 22.16.0.

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-course-"));
  try {
    const file = join(dir, "message.txt");
    await writeFile(file, "Read carefully", "utf8");
    console.log(await readFile(file, "utf8"));
  } finally { await rm(dir, { recursive: true, force: true }); }
}
main().catch(console.error);

Verified output

Read carefully

Compile: npx tsc --strict --target es2022 --module commonjs reading-writing-files.ts; run: node reading-writing-files.js. For Node.js API examples, install @types/node first. For browser projects, use the browser-specific instructions below.

The example runs in Node.js 22.16.0; if it reads runtime environment details, your displayed values may differ.

mkdtemp creates a unique temporary directory; writeFile stores the text; readFile returns a string with utf8 encoding. The finally block removes created files, including if an operation fails.

Predict what changes if you alter one input. Then run the code to compare your reasoning with the real output.

Avoid writing to fixed shared paths in examples; temporary directories prevent overwriting a user's real files.

Identify whether the failure is a type-checking issue, a configuration issue, or a runtime behavior issue before choosing a fix.

Write JSON representing a task list to a temporary file, read it back, and parse it using JSON.parse.

Write down your expected result first. For configuration examples, compare compiler output and diagnostics; for test examples, make the assertion fail deliberately to verify that the tool reports it.

The node:fs/promises API provides asynchronous filesystem operations such as readFile and writeFile.

Run the primary example, then complete the practice task or environment-specific lab.