Varuint (JavaScript / Deno / Browser)

日本語のREADMEはこちらです: README.ja.md

Varuint is an implementation of Unsigned Varint (LEB128-like, 7-bit + continuation bit) encoding and decoding. It can be used directly via URL import in Deno and the browser.

Features

• Varuint.encode(n) → Uint8Array
• Varuint.decode(bin, offset=0, wantBigInt=false) → number or BigInt (when wantBigInt=true)
• Varuint.length(n) → required byte length (number)

Usage

Browser / Deno (ESM)

import { Varuint } from "https://code4fukui.github.io/Varuint/Varuint.js";

const bin = Varuint.encode(300);
console.log(bin); // Uint8Array(2) [172, 2]

const n = Varuint.decode(bin);
console.log(n); // 300
const len = Varuint.length(n);
console.log(len); // 2

API

Varuint.length(n)

Returns the number of bytes required to represent n as a varuint.

console.log(Varuint.length(0));      // 1
console.log(Varuint.length(127));    // 1
console.log(Varuint.length(128));    // 2
console.log(Varuint.length(16384));  // 3

Varuint.encode(n)

Encodes n (a number or BigInt) into a Uint8Array.

• Supports number only for safe integers
• Use BigInt for larger values

console.log(Varuint.encode(300)); // Uint8Array [172, 2]
console.log(Varuint.encode(0));   // Uint8Array [0]

Varuint.decode(bin, offset = 0, wantBigInt = false)

Decodes a varuint from bin.

• Returns number by default
• Returns BigInt when wantBigInt=true
• Starts decoding from the given offset (useful for concatenated values)

const buf = new Uint8Array([9, 9, 172, 2, 9]);

console.log(Varuint.decode(buf, 2));        // 300
console.log(Varuint.decode(buf, 2, true));  // 300n

Note: If the decoded value exceeds Number.MAX_SAFE_INTEGER when wantBigInt=false, a RangeError will be thrown.

Format

• Stores 7 bits at a time from the least significant bit
• Sets the most significant bit (0x80) of each byte to 1 if the value continues
• The last byte has the MSB set to 0

Example:

• 300 → 0xAC 0x02 ([172, 2])

Deno test

deno test

License

MIT License — see LICENSE.