This set of questions are related to a project I've published for converting characters, or strings, to Hex based Unicode; eg...

//> 1f34d

toUnicode.fromString('Spam!', '0x');
//> ['0x53', '0x70', '0x61', '0x6d', '0x21']


  • Are there any mistakes, such as unaccounted for edge-cases?

  • Have I missed any test cases?

  • Any suggestions on making the code more readable and/or easier to extend?

  • Are there any features that are wanted?

Setup and Usage

The Source code is maintained on GitHub and may be cloned via the following commands. A Live demo is hosted online, thanks to GitHub Pages.

mkdir -vp ~/git/hub/javascript-utilities
cd ~/git/hub/javascript-utilities
git clone git@github.com:javascript-utilities/to-unicode.git

The build target is ECMAScript version 6, and so far both manual tests and automated JestJS tests show that the toUnicode methods function as intended; for both Browser and NodeJS environments.

Example NodeJS Usage

const toUnicode = require('./to-unicode.js');

var panda_code = toUnicode.fromCharacter('🐼');

//> '1f43c'

Source Code

I am concerned with improving the JavaScript, and TypeScript; ie. HTML is intended to be simple and functional.

'use strict';

 * Namespace for static methods that convert characters and strings to Unicode
class toUnicode {
     * Converts character to Hex Unicode
     * @param {string} character
     * @return {string}
     * @author S0AndS0
     * @copyright AGPL-3.0
     * @example
     * toUnicode.fromCharacter('🐼');
     * //> "1f43c"
    static fromCharacter(character) {
        return character.codePointAt(undefined).toString(16);

     * Converts string to character array of Unicode(s)
     * @param {string} characters
     * @return {string[]}
     * @author S0AndS0
     * @copyright AGPL-3.0
     * @example
     * toUnicode.fromString('🎉 👋');
     * //> [ '1f389', '20', '1f44b' ]
    static fromString(characters, prefix = '') {
        return [...characters].reduce((accumulator, character) => {
            const unicode = toUnicode.fromCharacter(character);
            return accumulator;
        }, []);

/* istanbul ignore next */
if (typeof module !== 'undefined') {
    module.exports = toUnicode;
<!DOCTYPE html>
<html lang="en" dir="ltr">
    <meta charset="utf-8">
    <title>toUnicode Usage Example</title>
    <script type="text/javascript" src="assets/js/modules/to-unicode.js" differ></script>

    <script type="text/javascript" differ>
      const text_input__callback = (_event) => {
        const client_input = document.getElementById('client__text--input').value;
        const client_prefix = document.getElementById('client__text--prefix').value;

        const output_element = document.getElementById('client__text--output');

        const unicode_list = toUnicode.fromString(client_input, client_prefix);
        output_element.innerText = unicode_list.join('\n');

      window.addEventListener('load', () => {
        const client_text_input = document.getElementById('client__text--input');
        const client_text_prefix = document.getElementById('client__text--prefix');

        client_text_input.addEventListener('input', text_input__callback);
        client_text_prefix.addEventListener('input', text_input__callback);

    <span>Prefix: </span>
    <input type="text" id="client__text--prefix" value="0x">


    <span>Input: </span>
    <input type="text" id="client__text--input" value="">

    <pre id="client__text--output"></pre>

JestJS Tests

For completeness here are the JestJS tests.

'use strict';

 * Tests modules within `to-unicode.js` script
 * @author S0AndS0
 * @copyright AGPL-3.0
class toUnicode_Test {
    constructor(min_code_point = 161, max_code_point = 1114111) {
        this.toUnicode = require('../to-unicode.js');
        this.min_code_point = min_code_point;
        this.max_code_point = max_code_point;

    randomCodePoint() {
        return Math.random() * (this.max_code_point - this.min_code_point + 1) + this.min_code_point | 0;

    runTests() {

     * Tests if `fromCharacter()` and `fromString()` functions are reversible.
    testInvariance() {
        const character_code_list = Array(99).fill(0).map((_) => {
            return this.randomCodePoint();

        let unicode_list = [];
        let characters_string = '';

        test('Is `fromCharacter()` reversible?', () => {
            character_code_list.forEach((code_point) => {
                const character = String.fromCodePoint(code_point);
                const unicode = this.toUnicode.fromCharacter(character);
                const decimal = Number(`0x${unicode}`);
                characters_string += character;

        test('Is `fromString()` reversible?', () => {

const test_toUnicode = new toUnicode_Test();

This is regarding the edge-cases and test cases mentioned in the question:

[...characters] // or Array.from(characters)

handles splitting the characters of string to an array in most of the cases. It is better than characters.split("") because it handles surrogate pairs pretty well.

console.log( "🍍".length ) // 2
console.log( [..."🍍"] )
console.log( "🍍".split("") )

What if you input something like 👨‍👩‍👧‍👦? You get


and not a single hex as output like before. Because, there are hundreds of emoji sequences which are combinations of multiple emojis but display as a single emoji. They are joined with a Zero Width Joiner (U+200D) character. When you use [...] on them, they are split into an array of individual emojis and joiner characters.

console.log("👁️‍🗨️".length) // 7

console.log("👨‍👩‍👧‍👦".length) // 11

Similarly, many languages create a grapheme or a symbol with combining marks. They look like distinctive units of writing, but are made up of multiple unicode points.

The below strings are not the same. The first string has á but the second string is a and a combining mark U+0301

const a = "álgebra",
      b = "álgebra"

console.log(a === b) // false
console.log(a.length, b.length)
console.log([...a].join(" , "))
console.log([...b].join(" , "))

console.log([..."हिन्दी"].join(" , ")) // Devanagari script

ि is a vowel sound and isn't used on it's own. It needs to be combined to with a consonant like (Ha) to get हि (He)

You can create big strings using multiple combining marks while the string looks like it has 6 distinct characters:

const a = 'Z͑ͫ̓ͪ̂ͫ̽͏̴̙̤̞͉͚̯̞̠͍A̴̵̜̰͔ͫ͗͢L̠ͨͧͩ͘G̴̻͈͍͔̹̑͗̎̅͛́Ǫ̵̹̻̝̳͂̌̌͘!͖̬̰̙̗̿̋ͥͥ̂ͣ̐́́͜͞'

console.log(a.length) // 75

The scenarios mentioned are not issues per se. You are basically converting the string to corresponding unicode hex. But, each grapheme or a symbol doesn't necessarily correspond to a single hex in the output. You can keep these in mind or add them to your edge cases / test cases.

Some further reading:

Also, codePointAt takes a number as a parameter.

return character.codePointAt(undefined).toString(16)

is same as

return character.codePointAt().toString(16)

Both of these work because if the argument is undefined, it defaults to 0. It's better to pass 0 explicitly as it is easily understandable. It wasn't clear why you were passing undefined initially.

return character.codePointAt(0).toString(16)
  • \$\begingroup\$ Thanks for the detailed answer!... Passing undefined to codePointAt was done to prevent TypeScript from complaining, but I'll certainly consider switching to 0 as that seems to be less confusing for readers (myself included)... As for Array.from(_string_) vs. [..._string_], so far tests seem to produce equivalent output, and last I read the spread syntax was the short-hand way of avoiding issues with String.split("") doing unkind things to non-ASCII strings. \$\endgroup\$ – S0AndS0 Aug 7 '20 at 0:36
  • 1
    \$\begingroup\$ @S0AndS0 sorry, I wan't clear in the answer. Array.from() and [...] are equivalent for a string input. They both use the Symbol.iterator property of the string to create an array. \$\endgroup\$ – adiga Aug 7 '20 at 5:10

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