Example PDF

var cell = [];
var w;
var numCells;
var numMines = 20;

function setup() {
  createCanvas(400, 400);
  numCells = 16;
  w = width/numCells;
  for(var i = 0; i < numCells; i++){
    let arr = [];
    for(var j = 0; j < numCells; j++){
      arr.push(new Cell(i,j));
    }
    cell.push(arr);
  }
  textSize(26);
  while(numMines > 0){
    let x = floor(random(numCells));
    let y = floor(random(numCells));
    if(!cell[x][y].isMine){
      cell[x][y].isMine = true;
      numMines--;
    }
  }
  countMines();
}

function draw() {
  background(220);
  for(var i = 0; i < numCells; i++){
    for(var j = 0; j < numCells; j++){
      cell[i][j].show();
    }
  }
}

function countMines(){
  for(var i  = 0; i < numCells; i++){
    for(var j = 0; j < numCells; j++){
      let c = 0;
      if(i>0 && j >0){
         if(cell[i-1][j-1].isMine){c++;}  //ROW ABOVE (j-1)
      }
      if(j>0){
        if(cell[i][j-1].isMine){c++;}
      }
      if(i<numCells-1 && j>0){
        if(cell[i+1][j-1].isMine){c++;}
      }
      if(i>0){
        if(cell[i-1][j].isMine){c++;}  //LEFT
      }
      if(i<numCells-1){
        if(cell[i+1][j].isMine){c++;}  //RIGHT
      }
      if(i>0 && j < numCells-1){
        if(cell[i-1][j+1].isMine){c++;}  //ROW BELOW (j+1)
      }
      if(j<numCells-1){
        if(cell[i][j+1].isMine){c++;}
      }
      if(i<numCells-1 && j < numCells-1){
        if(cell[i+1][j+1].isMine){c++;}
      }
      cell[i][j].count = c;
    }
  }
}

function mousePressed(){
  if(mouseX>0 && mouseX < width && mouseY >0 && mouseY<height){
    let x = floor(mouseX / w);
    let y = floor(mouseY / w);
    revealCell(x, y);
  }
}

function revealCell(x, y){
  cell[x][y].isRevealed = true;
  if(cell[x][y].isMine){
    revealAll();
  }
  if(cell[x][y].count == 0){
    //CELLS ABOVE
    if(x>0 && y>0){
      revealCell(x-1, y-1);
    }
    if(y>0){
      revealCell(x, y-1);
    }
    if(x+1 < numCells-1 && y>0){
      revealCell(x+1, y-1);
    }

    //Side CELLS
    if(x>0){
      if(!cell[x-1][y].isRevealed){
        revealCell(x-1, y);
      }
    }
    if(x<numCells-1){
      if(!cell[x+1][y].isRevealed){
        revealCell(x+1, y);
      }
    }

    //CELLS BELOW
    if(x>0 && y < numCells-1){
      if(!cell[x-1][y+1].isRevealed){
        revealCell(x-1, y+1);
      }
    }
    if(y<numCells-1){
      if(!cell[x][y+1].isRevealed){
        revealCell(x, y+1);
      }
    }
    if(x<numCells-1 && y<numCells-1){
      if(!cell[x+1][y+1].isRevealed){
        revealCell(x+1, y+1);
      }
    }
  }
}

function revealAll(){
  for(var i = 0; i < numCells; i++){
    for(var j = 0; j < numCells; j++){
      cell[i][j].isRevealed = true;
    }
  }
}
class Cell{
  constructor(x, y){
    this.x = x;
    this.y = y;
    this.hasMine = false;
    this.count = 0;
    this.isMine = false;
    this.isRevealed = false;
  }

  show(){

    if(this.isRevealed){
      if(this.isMine){
        fill(0,0,255);
      } else {
        fill(255);
      }
      rect(this.x*w, this.y*w, w, w);
      fill(0);
      text(this.count, this.x*w+w/4 + 2, this.y*w + 3*w/4);
    } else {
      fill(220);
      rect(this.x*w, this.y*w, w, w);
    }
    //text(this.x, this.x*w, this.y*w+w/2);
  }
}