js-tetris - count lines

board.js

clearLines() {
  let lines = 0;
  this.board.forEach((row, y) => {    
    if (row.every(value => value !== 0)) {      
      lines++; // Increase for cleared line
      this.board.splice(y, 1); 
      this.board.unshift(Array(COLS).fill(0));
    }  
  });  
  if (lines > 0) {    
    // Add points if we cleared some lines
    account.score += this.getLineClearPoints(lines);  
  }
}