By the end of this lesson
Create a practice text file without overwriting an existing file.
Before you start
- Node.js 24 with a terminal and plain-text editor; the browser-only lesson is labelled separately.
- Complete lesson 18 or be comfortable with its examples.
Three words to know
- Working directory
- The folder from which relative data paths are resolved.
- UTF-8
- An encoding for storing text as bytes.
- Exclusive creation
- Creating a new file only when the path does not already exist.
1. Use a fresh practice folder
The .mjs example below runs in Node and creates notes.txt in the process’s current working folder. It is not relative to the source file merely because you placed them together. Keep this exercise separate from important files. Node APIs use node: imports; this source will not run as a browser script.
import { readFile, writeFile } from "node:fs/promises";
await writeFile("notes.txt", "Read\nTest\n", { encoding: "utf8", flag: "wx" });
const contents = await readFile("notes.txt", "utf8");
console.log(contents.trimEnd());
What you should see · example output
Read Test
2. Preserve a useful failure
The wx flag requests exclusive creation, so a second run in the same folder fails instead of overwriting notes.txt. Inspect the first file, choose a fresh folder or intentionally choose a new name. The default write behaviour can replace content, so do not remove wx just to hide the error.
3. Convenience is not a bounded reader
readFile reads the full file and decoding with utf8 can replace malformed byte sequences. That is convenient for this small trusted practice text, not a strict untrusted-input validator. The final project performs a bounded byte read and uses a fatal TextDecoder instead. File permissions, slow storage and special files also need separate consideration.
YOUR TURN
A small check before you continue
Why does the second execution fail? Should you add a catch that prints an empty document?
Show a suggested answer
Exclusive creation rejects the existing path. An empty result would hide the real failure. Inspect the existing file and decide deliberately whether to keep it or choose another practice filename.
Sources and scope
Documentation and examples reviewed 2026-10-18. Provider screens, package versions and output wording can differ. Examples show expected outcomes; they are not a claim that OpenViST connected to your server or verified your setup.