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A thorough knowledge of Javascript can give you tremendous control over what happens on a website. Combined with PHP through an AJAX request, you can make some pretty nifty browser-based games.

This tutorial will focus on the first part of making a basic board game - creating a board. The end result will be a three by three game board suitable for use in developing a tic-tac-toe game.

Game Development with JS, AJAX, and PHP

How can we use JS and PHP - connected through AJAX - to develop an online game?

Javascript’s main use for us is to create an interface for the game. Through Javascript we can capture user input - i.e. mouse clicks and text. We can also alter the game’s output - changing the HTML of the page, adding images, and moving things around. Javascript will provide a lot of the front end work.

PHP, on the other hand, is a more robust language for dealing with the logic of the game. PHP could be useful for developing an AI and evaluating winning conditions. It also offers a great way to store information for later use through flat files or database integration.

If we’re going to use both Javascript and PHP, we’ll need to use AJAX. This is the glue that holds the whole thing together. It will send input from the main Javascript to the PHP processing scripts. The PHP script will then send info back to the Javascript and it will alter the page’s layout accordingly.

Step One: Building a Game Board

The first step in creating a graphical online game is to build a game board. The most basic board I could think of - and therefore a good starting point - is a tic-tac-toe board.

First, we should define and create our basic building block. A square.

In terms of HTML/CSS, our square will be a div tag. We’ll be able to position and style it to our liking, and we can add javascript triggers like “onClick” to help run our Javascript.

Our first box is going to be a simple 50px x 50px square. When you click it, it will change background colors to black.

Here’s the CSS we’ll use for the square.

.box {
  width: 50px;
  height: 50px;
  border: thin solid black;
}

Inside the html body we can create our box like this.

<div class="box" id="box" onClick="makeBlack();"></div>

Finally, we need to define our Javascript function makeBlack(). We’ll access the div element through it’s ID (’box’) and change it’s background style to be black.

function makeBlack() {
  var box = document.getElementById('box');
  box.style.background = 'black';
}

Now we’ve got a building block! We just successfully used Javascript and DOM to create a click-able box. With some tweaking, we can turn this into a nifty 3×3 grid for Tic Tac Toe.

Step Two: Build a Grid

For Tic Tac Toe, we’re going to need a 3×3 grid. We can modify our CSS a bit and create 9 separate divs to accomplish this. Add the following lines to the CSS for .box, and create a new class .break.

.box {
  float: left;
}
 
.break {
  clear: bloth;
}

This way our boxes line up in a row. If we include a “break” class in our div, we can start a new line. Therefore we should update the html like this.

<div class="box break" id="one" onClick="makeBlack('one');">1</div>
<div class="box" id="two" onClick="makeBlack('two');">2</div>
<div class="box" id="three" onClick="makeBlack('three');">3</div>
<div class="box break" id="four" onClick="makeBlack('four');">4</div>
<div class="box" id="five" onClick="makeBlack('five');">5</div>
<div class="box" id="six" onClick="makeBlack('six');">6</div>
<div class="box break" id="seven" onClick="makeBlack('seven');">7</div>
<div class="box" id="eight" onClick="makeBlack('eight');">8</div>
<div class="box" id="nine" onClick="makeBlack('nine');">9</div>

Notice that each box has it’s own unique ID - one to nine. I also changed the makeBlack() function to include a parameter - an ID. Let’s update the makeBlack() function to utilize this to change the specific box that we click on.

function makeBlack (boxId) {
  var box = document.getElementById(boxId);
  box.style.background = 'black';
}

Step Three: Use a Background Image Instead of a Background Color

Turning a box to a black background color isn’t that impressive. But it’s easy to use as a demonstration.

For a game, it would be much more useful to make an image appear in our div. We can do that by editing the “background” style of the div in the makeBlack() function. Note: You might also want to change the name of the function to something more descriptive, like changeBackground().

Here’s how to do it.

function changeBackground (boxId) {
  var box = document.getElementById(boxId);
  box.style.background = 'transparent url(image.png) top left no-repeat';
}

The property “box.style.background” accesses the “background” css style for the “box” id. Give it a value just like you would in a css stylesheet. In this case, we’re giving it a background of “image.png.” You might want to change this to a “circle.png” or a “cross.png” that you create for your game.

Step Four: Changing the onClick Event

The last thing we want to look at in this introduction is how to change the onClick event for our div. You might want to get rid of it altogether - or maybe change it to a new function. For example, after turning the box black, you might want to make the onClick call a new function - makeWhite().

We can do this through another DOM method, similar to the way we accessed the styles before. Assuming we have the same variable box that refers to our div, here’s what we need to do in our function.

//  Get rid of onClick altogether
box.removeAttribute('onClick');
 
//  Change onClick to a new function
box.setAttribute('onClick', 'makeWhite();');

Where To Go From Here?

Now that you’ve got a basic 3×3 grid and you know how to make it respond to user input, you can get started on making a game.

Here are a few of the things you’ll want to think about next.

• I need some images to place in my boxes.
• How Can I Alternate Players (and images)?
• How Can I Determine Who Wins?
• How Can I Make the Computer Play (AI!)?

You can go ahead and get started on your own - but I’ll certainly return to this topic within the next week or two with some more examples. After the next tutorial, we’ll have a working Tic-Tac-Toe board driven solely by Javascript.

Tags: design, dom, game, graphics, input, js