adventofcode_day6.js

const findSignal = (count, inputString) => {
    const inputChars = inputString.split('')
    const markerStartIdx = inputChars.findIndex((_, idx) => {
        const chars = inputChars.slice(idx, idx + count);
        const set = new Set(chars);
        if (set.size === count) {
            return true;
        }
    })
    return markerStartIdx + count;
}

console.log(
    findSignal(4, inputString),
    findSignal(14, inputString)
);