Compress JS strings for fun and profit

compress.ts

const maxCharCode = 2 ** 16 - 1;

export function compress(input: string): string {
    let output = "";
    for (let pos = 0; pos < input.length; pos++) {
        const maxLookBack = Math.min(pos, maxCharCode);
        let didOutputMatch = false;
        let charsToSkip = 0;
        for (let back = 0; back < maxLookBack; back++) {
            let backLen = 0;
            let isMatching = false;

            const maxBackLen = Math.min(input.length - pos, back);
            // Compare backstring and posstring
            while (backLen < maxBackLen) {
                if (input[pos - back + backLen] === input[pos + backLen]) {
                    isMatching = true;
                    backLen++;
                } else {
                    break;
                }
            }

            // If has a match, write it and keep going
            if (isMatching && backLen > 3) {
                output += '\0';
                output += String.fromCharCode(back);
                output += String.fromCharCode(backLen);

                didOutputMatch = true;
                charsToSkip = backLen - 1;
                break;
            }
        }

        if (!didOutputMatch) {
            output += input[pos];
        }
        pos += charsToSkip;
    }

    return output;
}

export function uncompress(input: string): string {
    let output = "";

    for (let pos = 0; pos < input.length; pos++) {
        const char = input[pos];
        if (char === '\0') {
            const back = input.charCodeAt(pos + 1);
            const backLen = input.charCodeAt(pos + 2);
            const delta = output.slice(
                output.length - back,
                output.length - back + backLen
            );
            output += delta;
            pos += 3 - 1;
        } else {
            output += char;
        }

    }

    return output;
}