JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main"></div>

JavaScript

function init(){
  //board init
  var width = parseInt(prompt ("Width?", "10")),
      height = parseInt(prompt ("Height?", "10")),
      board = [];

  for (var i = 0; i <= height; i++) {
    board[i] = [];
    for (var k = 0; k <= width; k++) {
      board[i][k] = {};
    }
  }

  //init html board
  for (var a = 0; a < board.length; a++){
    //create parent div + pick him style
    var divRow = document.createElement("div");
    divRow.className = "row";

    var parentElementRow = document.querySelector(".main");
    parentElementRow.appendChild(divRow);

    for (var c = 0; c < board[a].length; c++){
      // create child div + pick him style
      var divCol = document.createElement("div");
      divCol.className = "col";
      var parentElementCol = document.querySelector(".main").lastChild;
      parentElementCol.appendChild(divCol);
    }
  }
}

init();