isutf8

isutf8

Deprecated: Use isUtf8 from node:buffer in Node.js, or TextDecoder with { fatal: true } in browsers. See the migration examples below.

Quick check if a Node.js Buffer or Uint8Array is valid UTF-8.

Advantages

• Ultra-small package size
• No runtime dependencies
• No native compilation required

Migration to built-in APIs

For modern Node.js applications, prefer the built-in isUtf8 from node:buffer, available since Node.js 18.14.0 and 19.4.0:

import { isUtf8 } from 'node:buffer';

console.log(isUtf8(Buffer.from([0xd0, 0x90]))); // true

In modern browsers, use TextDecoder with fatal: true to reject invalid UTF-8:

function isUtf8(input) {
  if (input === undefined) return false;

  try {
    new TextDecoder('utf-8', { fatal: true }).decode(input);
    return true;
  } catch (error) {
    if (error instanceof TypeError) return false;
    throw error;
  }
}

console.log(isUtf8(new Uint8Array([0xd0, 0x90]))); // true
console.log(isUtf8(new Uint8Array([0xc3]))); // false

Unlike a byte-only validator, TextDecoder also produces a decoded string. This package mainly remains useful for older environments without these APIs (it supports Node.js 12 or later), or for retaining its existing API. When migrating, note that this package returns false for a missing argument, while Node.js's built-in isUtf8 throws a TypeError.

Install

npm install isutf8

Usage

CommonJS

const isUtf8 = require('isutf8');

const buf = Buffer.from([0xd0, 0x90]);
console.log(isUtf8(buf)); // true

// or

const arr = new Uint8Array([0xd0, 0x90]);
console.log(isUtf8(arr)); // true

ES Modules or TypeScript

import isUtf8 from 'isutf8';

const buf = Buffer.from([0xd0, 0x90]);
console.log(isUtf8(buf)); // true

// or

const arr = new Uint8Array([0xd0, 0x90]);
console.log(isUtf8(arr)); // true

API

isUtf8(input?: Buffer | Uint8Array): boolean

Returns true for valid UTF-8 byte sequences, including ASCII and empty input. Returns false for invalid or incomplete sequences, or a missing argument. It validates bytes; it does not detect the original encoding or decode text.

const isUtf8 = require('isutf8');

console.log(isUtf8(new Uint8Array())); // true
console.log(isUtf8(new Uint8Array([0xc3]))); // false: incomplete sequence
console.log(isUtf8()); // false

Development

Use Node.js 22.13.0 or later in the Node.js 22 line, or Node.js 24 or later, for the development tools.

npm ci
npm test
npm run build

TypeScript is kept on 6.0.x because the current typescript-eslint and ts-jest releases do not support TypeScript 7 yet.

License

MIT License