sparse matrix multiplication

gistfile1.txt

function matrixMultiplication (matrixA, matrixB) {
    const matrixC = matrixA.map(x => matrixB[0].map(y => 0));
    const lengthR = matrixA.length
    const lengthC = matrixA[0].length
    const lengthB = matrixB[0].length
    let k = 0
    for (let i = 0; i < lengthR; i++) {
        k = 0
        for (let j = 0; j < lengthB; j++) {
            if(matrixA[i][j] === undefined || matrixB[j][k] === undefined)
                continue
            if(k === lengthB)
                break;
            if(matrixA[i][j] !== 0 && matrixB[j][k] !== 0)
                  matrixC[i][k] += matrixA[i][j] * matrixB[j][k]
            if(j === lengthC - 1) {
                j = -1;
                k++;
            }
        }
    }
    return matrixC;
}