2D Array

spiral.js

function layerTopRight(matrix) {
  
  // remove and store the first row from matrix
  var top = matrix.splice(0, 1);
  
  // store the right column of the matrix
  var right = [];
  
  // remove the last column from the matrix
  for (var i = 0; i < matrix.length; i++) {
    var e = matrix[i].splice(-1, 1);  
    right.push(e);
  }
  
  // return the top row and last column elements as a list
  return top.concat(right).toString().split();
  
}

function layerBottomLeft(matrix) {
  
  // remove and store the last row from matrix in reverse order
  var bottom = matrix.splice(matrix.length-1, 1)[0].reverse();
  
  // store the left column of the matrix
  var left = [];
  
  // remove the first column from the matrix
  for (var i = 0; i < matrix.length; i++) {
    var e = matrix[i].splice(0, 1);  
    left.push(e);
  }
  
  // return the top row and last column elements as a list
  return bottom.concat(left.reverse()).toString().split();
  
}

// our main spiral function that will
// return a final spiral ordered list
function spiral(matrix) {
  
  // where we store our final spiraled list
  var spir = [];
  
  while (matrix.length > 0) {
    
    // if only 1 more element left in matrix
    if (matrix.length === 1) { 
      spir.push(matrix[0]); 
      break;
    }
    
    // return the spiraled list of the top row and
    // right column for this matrix
    var tr = layerTopRight(matrix);
    spir.push(tr);
    
    // return the spiraled list of the bottom row and
    // left column for this matrix
    var bl = layerBottomLeft(matrix);
    spir.push(bl);

  }
  
  return spir.toString().split();
  
}

// setup a matrix
var M = [[1, 2, 3, 4], 
         [4, 5, 6, 7,9,12], 
         [7, 8, 9, 10,11]];

// return it in spiral order
spiral(M);