hill.js

const hill = (text, matrix) => {

    if (text.length % matrix.length != 0) {
        throw "please provide a plaintext that can be cleanly divided into " + matrix.length + " parts"
    }

    const chunks = [];
    for (let i = 0; i < text.length; i += matrix.length) {
        chunks.push(text.substring(i, i + matrix.length));
    }

    const ciphertext = chunks.map(chunk => chunk.split(''))
        .map(splitChunk => [splitChunk.map(letter => letterDict[letter])])
        .map(transpose)
        .map(transposedChunk => {
            console.log(matrix);
            return modMatrix(
                matrixMultiply(matrix, transposedChunk), 
                letters.length
            );
        })
        .map(transpose)
        .map(splitChunk => splitChunk[0].map(num => letters[num]))
        .map(chunk => chunk.join(''))
        .join('');

    return {
        plaintext: text,
        ciphertext: ciphertext,
        solution: matrix
    }
}