code: function makeMatrix(n, m, x) {
    var matrix = [];
    for (var i = 0; i < n; i++) {
      matrix[i] = new Array(m);
      for (var j = 0; j < m; j++) {
        matrix[i][j] = x;
      }
    }
  
    return matrix;
  }
docs: Returns a two-dimensional array (an array of arrays) with dimensions n by m.
  All the elements of this new matrix are initially equal to x
  @param n number of rows
  @param m number of columns
  @param x initial element for every item in matrix