Quick encrypt and decrypt methods für vigenere ciper

vigenere-cipher.js

const Alphabet = `ABCDEFGHIJKLMNOPQRSTUVWXYZ`.split("");
const isEqualWith = key => v => key === v;

const matchKeyWithText = (key, text) =>
    text
        .split("")
        .map((_, i) => key[i % key.length])
        .join("");

const decode = key => text => {
    const keytext = matchKeyWithText(key, text);
    let result = "";
    for (let i = 0; i < text.length; i++) {
        const textIndex = Alphabet.findIndex(isEqualWith(text[i]));
        const keyIndex = Alphabet.findIndex(isEqualWith(keytext[i]));

        let realIndex = textIndex - keyIndex;
        if (realIndex < 0) realIndex += Alphabet.length;
        result += Alphabet[realIndex];
    }
    return result;
};

const encrypt = key => text => {
    const keytext = matchKeyWithText(key, text);
    let result = "";
    for (let i = 0; i < text.length; i++) {
        const textIndex = Alphabet.findIndex(isEqualWith(text[i]));
        const keyIndex = Alphabet.findIndex(isEqualWith(keytext[i]));
        let realIndex = (textIndex + keyIndex) % Alphabet.length;
        result += Alphabet[realIndex];
    }
    return result;
};

encrypt("KEY")("DCODE"); //?
decode("KEY")("NGMNI"); //?