@technobuddha/library/encodeUTF8/encodeUTF8.ts

A large library of useful functions

import { empty } from '../constants';

/**
 * Encode a unicode (UTF-16 encoded javascript) string into UTF8
 *
 * @param input The string to encode
 * @returns The UTF-8 encoded string
 */
export function encodeUTF8(input: string): string {
    let result = empty;

    for(let i = 0; i < input.length; ++i) {
        let c0 = input.charCodeAt(i);

        if(c0 < 0x0080) { result += input[i]; } else if(c0 < 0x0800) { result += String.fromCharCode(c0 >> 6 | 0xC0) + String.fromCharCode(c0 & 0x3F | 0x80); } else if(c0 >= 0xD800 && c0 < 0xDC00) {
            if(++i >= input.length)
                throw new Error(`Incomplete surrogate pair @${i}`);

            const c1 = input.charCodeAt(i);
            if(c1 < 0xDC00 || c1 > 0xDFFF)
                throw new Error(`Invalid surrogate pair @${i}`);

            c0 = 0x10000 + ((c0 & 0x03FF) << 10) + (c1 & 0x03FF);
            result += String.fromCharCode((c0 >> 18) | 0xF0) +
                String.fromCharCode(((c0 >> 12) & 0x3F) | 0x80) +
                String.fromCharCode(((c0 >> 6) & 0x3F) | 0x80) +
                String.fromCharCode((c0 & 0x3f) | 0x80);
        } else {
            result += String.fromCharCode((c0 >> 12) | 0xE0) +
                String.fromCharCode(((c0 >> 6) & 0x3F) | 0x80) +
                String.fromCharCode((c0 & 0x3F) | 0x80);
        }
    }

    return result;
}

export default encodeUTF8;