maze.js

var WIDTH = 10
var HEIGHT = 10
// 0 is null, pointers start at 1
const SIZE = WIDTH * HEIGHT
var set = new Uint16Array(SIZE)

// return end of chain
function walk(a) {
  while (set[a - 1]) {
    a = set[a - 1]
  }
  return a
}

// return true if they were different and we merged them
function merge(a, b) {
  a = walk(a)
  b = walk(b)
  if (a == b) return 1;
  set[a - 1] = b
  return 0
}

var wall_order = new Uint16Array(SIZE * 2)
var walls = new Uint16Array(SIZE * 2)
for (var i = 0; i < SIZE * 2; i++) {
  wall_order[i] = i
}

// Shuffle Shuffle
for (var i = 0; i < SIZE * 2; i++) {
  var b = Math.floor(Math.random() * SIZE * 2)
  var temp = wall_order[i]
  wall_order[i] = wall_order[b]
  wall_order[b] = temp;
}

for (var i = 0; i < SIZE * 2; i++) {
  var index = wall_order[i]
  var a, b
  if (index < SIZE) { // first set are right walls
    a = index + 1
    // skip right walls on right side
    if ((a % WIDTH) == 0) {
      b = a
    } else {
      b = a + 1
    }
  } else { // next set are bottom walls
    a = index - SIZE + 1
    // skip bottom walls on bottom side
    if (a + WIDTH > SIZE) {
      b = a
    } else {
      b = a + WIDTH
    }
  }
  walls[index] = merge(a, b)
}

var icons = [" ▄", " █", "▄▄", "▄█"]

var lines = []
for (var y = -1; y < HEIGHT; y++) {
  var line = ""
  for (var x = -1; x < WIDTH; x++) {
    var index
    if (y == -1 && x == -1) {
      index = 0
    } else if (y == -1) {
      index = 2
    } else if (x == -1) {
      index = 1
    } else {
      var i = x + y * WIDTH
      index = walls[i] + walls[i + SIZE] * 2
    }
    line += icons[index]
  }
  lines.push(line)
}
console.log(lines.join("\n"))