Create JS 2D Array with default value

function matrix( rows, cols, defaultValue){

  var arr = [];

  // Creates all lines:
  for(var i=0; i < rows; i++){

      // Creates an empty line
      arr.push([]);

      // Adds cols to the empty line:
      arr[i].push( new Array(cols));

      for(var j=0; j < cols; j++){
        // Initializes:
        arr[i][j] = defaultValue;
      }
  }

return arr;
}