sketch.js

let cols, rows;
let w = 20;
let grid = [];
let current;
let stack = [];
function setup() {

  createCanvas(600, 600);
  cols = floor(width/w);
  rows = floor(height/w);

  for(let j=0;j<rows;j++) {
    for(let i=0;i<cols;i++) {
        var cell = new Cell(i,j);
        grid.push(cell);
    }
  }
  current = grid[0];
}

function draw() {
  background(51);
  for(let i=0;i<grid.length;i++) {
    grid[i].show();
  }
  current.visited = true;
  current.highlight();
  let next = current.checkNeighbors();
  if(next) {
    next.visited = true;
    stack.push(current);
    removeWalls(current,next);
    current = next;
  } else if(stack.length>0) {
    current = stack.pop();
  }

}

function index(i,j) {
  if(i<0 || j<0 || i>cols-1 || j>rows-1)
    return -1;
  return i + j*cols;
}

function removeWalls(a, b) {
  let x = a.i - b.i;
  if (x === 1) {
    a.walls[3] = false;
    b.walls[1] = false;
  } else if (x === -1) {
    a.walls[1] = false;
    b.walls[3] = false;
  }
  let y = a.j - b.j;
  if (y === 1) {
    a.walls[0] = false;
    b.walls[2] = false;
  } else if (y === -1) {
    a.walls[2] = false;
    b.walls[0] = false;
  }
}