I know there are a lot of posts for Angular, so I will spare everyone a rehash of setup and Hello World. Instead, I thought it would be fun to show a simple example of Angular recreating Conway’s Game of Life.
This example will use the following technologies:
- HTML
- CSS
- Angular.js
- Bootstrap
If you would like to see a sample of the working application, click here: http://www.nicholasbarger.com/demos/conways-game-of-life.
What is Conway’s Game of Life
Check out Wikipedia: http://en.wikipedia.org/wiki/Conway%27s_Game_of_Lifefor a more in depth definition and origin of the game, but in short, it’s a simulation that allows you to observe evolutions based on an initial starting configuration while applying the following four basic rules at each round:
- Any live cell with fewer than two live neighbors dies, as if caused by under-population.
- Any live cell with two or three live neighbors lives on to the next generation.
- Any live cell with more than three live neighbors dies, as if by overcrowding.
- Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction.
The game can continue indefinitely resulting in either a repeating pattern or a “still life” where no more moves can occur.
Since this article is more about Angular, I’ve simplified the game a bit as well to randomly select the starting positions and limited the board to 30 by 30 cells, but feel free to improve the code to allow the gamer to specify starting positions or infinite space. All source code can be found here: https://github.com/nicholasbarger/conways-game-of-life.
Let’s set up the UI
To start, let’s set up a form and board to play on. The form is pretty straightforward and allows you to specify the number of starting life forms, how many generations to simulate and finally, a button to start the game.
Enter the number of spontaneous lifeforms:
Enter the number of generations to simulate:
Start
Notice, that we’re using a few Angular tags to collect the data and fire off the game.
First, the data to interact with is wrapped with a div that specifies an ng-controllerattribute. This attribute is used to specify what controller will be used to execute logic against the HTML DOM elements. It is common to place this controller logic in another Javascript file.
Next, ng-submitis used to specify what function will be called on the controller when the form is submitted. When we wire up the controller, this is the method that will start iterating over generations in the game.
Finally, ng-modelis used to bind data values from the input form fields into variables that can be accessed in the controller. When the values on the form are changed, the variables backing them are automatically notified of the change and updated.
Now that we have a form created to gather some basic information about starting the game, let’s create the board that the game will actually play on.
<strong ng-show="rows.length > 0">Generation </strong>
<table id="board" class="table table-bordered">
<tr ng-repeat="row in rows">
<td ng-repeat="cell in row">
<i class="glyphicon glyphicon-fire" ng-show="cell.isAlive == true"></i>
</td>
</tr>
</table>
In this code snippet, we see a few new Angular components used for controlling presentation of data.
First, ng-showallows us to toggle the visibility of DOM elements by evaluating a true/false statement. Essentially, when the expression is true, we’re setting a CSS style “display: block”, and when false, setting “display: none”.
Next, we get our first look at the mustache-inspired template rendering (http://mustache.github.io) used by Angular. Notice the double curly braces surrounding the variable name in . This allows rendering of this variable and is automatically updated whenever the value of the variable changes.
The Angular control we have not yet covered is ng-repeatand is used when building out the table as we create rows and cells based on the number of items in the “rows” variable. This simply iterates over the collection and continues to generate the content where the attribute is specified and all information that is a child within it.
Finally, we revisit the ng-show attribute to show a small icon in the cell based on whether it is alive or dead. The “== true” is a bit redundant (and admittedly, should be “===” if used anyway to strictly check the value).
Wire up the Controller to Play
The controller is just a function that sets up all of the code to interact with the UI and exposes the necessary variables through a special parameter called $scope. You can read quite a bit more on $scope through the Angular documentation https://docs.angularjs.org/guide/scopebut for simplicity, it’s a way to expose variables to binding in the UI.
If the UI is going to use a variable or call a function, it must be attached to $scope through the following syntax:
$scope.myVariable = ‘Some value’;
$scope.myFunction = function(param1, param2) { return param1 + param2; };
For brevity sake, I will just link to the file hosted on Github since its code is not truly Angular specific and mostly controls running the game. I’ve attempted to comment the rules fairly well so it is evident what is happening in each “generation” of the game. https://github.com/nicholasbarger/conways-game-of-life/blob/master/game.html
Take Away
At my company, we’ve adopted Angular to use every day in production development and haven’t looked back. The benefits of creating a single page applications (SPA) which limits full trips back and forth on the server has allowed us to provide a more native experience over the web while reducing our server load by pushing some of the processing back onto the client.
The example shown in this article is by no means production code and is structured all in one file, which is usually not appropriate for production use. Enterprise level applications need to fully utilize separation into various modules that are comprised of controllers, views, partials, directives, services, and so on.
I’ve learned to stop promising future blog posts since I tend to write in short waves and then neglect my blog for months at a time; however, I think it would be great to write several posts on architecting large Angular web applications and some of the challenges we have faced. Stay tuned (but don’t hold your breath)!
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