Rotate (right or left) a 2D matrix implemented as a 1D array. Also it should be noted that this is called "transpose" in the math world.

rotate-one-dimensional-array.js

// You can adjust these params to suit your actual dimensions
const width = 10;
const height = 10;

const idx = (y, x) => y * height + x

// GIVEN:
// const matrix1D = [0,1,2,3, /* ... */, 98,99]
// const matrix2D = [
//   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
//   // ...
//   [90, 91, 92, 93, 94, 95, 96, 97, 98, 99],
// ];
//
// THEN:
// matrix1D[idx(2,3)] === matrix2D[2][3]

// ==================================================================

function rotateOverDiagonal(matrix) {
  const copy = [...matrix]
  for(let x = 0; x < height; ++x) {
    for(let y = 0; y < x; ++y) {
      let temp = copy[idx(x,y)];
      copy[idx(x,y)] = copy[idx(y,x)];
      copy[idx(y,x)] = temp;
    }
  }
  return copy
}

function rotateRight (matrix) {
  const copy = rotateOverDiagonal(matrix)
  
  // rotate over the column center clockwise
  for (let x = 0; x < width; ++x) {
    for (let y = 0; y < height / 2; ++y) {
      const temp = copy[idx(x,y)];
      copy[idx(x,y)] = copy[idx(x,width - y - 1)];
      copy[idx(x,width - y - 1)] = temp;
    }
  }
  return copy
}

function rotateLeft (matrix) {
  const copy = rotateOverDiagonal(matrix)
  
  // rotate over the column center counter-clockwise
  for (let x = 0; x < width; ++x) {
    for (let y = 0; y < height / 2; ++y) {
      const temp = copy[idx(x,y)];
      copy[idx(x,y)] = copy[idx(x,(width + y) % width)];
      copy[idx(x,(width + y) % width)] = temp;
    }
  }
  return copy
}

// ==================================================================

console.log(rotateRight([
      0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
     10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
     20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
     30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
     40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
     50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
     60, 61, 62, 63, 64, 65, 66, 67, 68, 69,
     70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
     80, 81, 82, 83, 84, 85, 86, 87, 88, 89,
     90, 91, 92, 93, 94, 95, 96, 97, 98, 99,
])) // -->
// [
//   90, 80, 70, 60, 50, 40, 30, 20, 10, 0,
//   91, 81, 71, 61, 51, 41, 31, 21, 11, 1,
//   92, 82, 72, 62, 52, 42, 32, 22, 12, 2,
//   93, 83, 73, 63, 53, 43, 33, 23, 13, 3,
//   94, 84, 74, 64, 54, 44, 34, 24, 14, 4,
//   95, 85, 75, 65, 55, 45, 35, 25, 15, 5,
//   96, 86, 76, 66, 56, 46, 36, 26, 16, 6,
//   97, 87, 77, 67, 57, 47, 37, 27, 17, 7,
//   98, 88, 78, 68, 58, 48, 38, 28, 18, 8,
//   99, 89, 79, 69, 59, 49, 39, 29, 19, 9
// ]

console.log(rotateLeft([
     0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
    10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
    20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
    30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
    40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
    50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
    60, 61, 62, 63, 64, 65, 66, 67, 68, 69,
    70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
    80, 81, 82, 83, 84, 85, 86, 87, 88, 89,
    90, 91, 92, 93, 94, 95, 96, 97, 98, 99,
])) // -->
// [
//   0, 10, 20, 30, 40, 50, 60, 70, 80, 90,
//   1, 11, 21, 31, 41, 51, 61, 71, 81, 91,
//   2, 12, 22, 32, 42, 52, 62, 72, 82, 92,
//   3, 13, 23, 33, 43, 53, 63, 73, 83, 93,
//   4, 14, 24, 34, 44, 54, 64, 74, 84, 94,
//   5, 15, 25, 35, 45, 55, 65, 75, 85, 95,
//   6, 16, 26, 36, 46, 56, 66, 76, 86, 96,
//   7, 17, 27, 37, 47, 57, 67, 77, 87, 97,
//   8, 18, 28, 38, 48, 58, 68, 78, 88, 98,
//   9, 19, 29, 39, 49, 59, 69, 79, 89, 99
// ]

@drewswaycool let me know if you have any questions. If you wanted in-place swapping just replace the copy vars for matrix in the functions.