Convert Numbers to Hexadecimal Strings in JavaScript

When developing in multiple languages, even simple routines can be easy to forget.
This note summarizes how to convert numbers into hexadecimal strings in JavaScript.

Contents

Basic Conversion Using toString(16)
Hex Conversion with Zero‑Padding
1. Utility Function
2. Examples

Basic Conversion Using toString(16)

javascript

var i = 15;
var s = i.toString(16); // "f"

var i = 255;
var s = i.toString(16); // "ff"

Hex Conversion with Zero‑Padding

「数値を16進数表記の文字列に変換。(ゼロ埋め)」（PDFより引用）

Utility Function

javascript

function toHex(num, fm) {
    // Convert number to hex string
    var s = num.toString(16);

    // If no format is provided, return raw hex
    if (fm === undefined) return s;

    // Determine current hex length
    var dLen = s.length;

    // Zero‑pad based on format length
    s = Array(fm.length - dLen + 1).join('0') + s;

    return s;
}