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Javascript Variables And DataTypes

To get started in game development you should have some basic knowledge of JavaScript. The best way to learn is through game programming examples. To do that we are going to start with Variables and Datatypes.


Variables are named containers that store data in a program. You can store the player stats, scores or game object locations. Before being able to use a variable they must be declared first in JavaScript. To do that you simply add the keyword var in front of the variable you want to create.

var characterName;
var score;

Variables can be given almost any name except for a few rules:

  • You cannot use JavaScript reserved keywords as a variable name. I created a full list infographic here.
  • Names cannot start with a number, but they can be added anywhere else in the name!
  • They are also case-sensitive, meaning “weapon” and “Weapon” are two different variables.

Another thing to note is you only need to declare a variables once.

For example:

var characterName = "Rich"; // Declare the variable characterName with the name Rich

characterName = "Steve";  //  Lets not go with Rich but lets change it to Steve!

Notice when I wanted to change the name I put in the variable characterName I did not put the keyword var in front of it.


There are six primitive datatypes:

  • Numbers
  • Strings
  • Booleans
  • Null
  • Undefined
  • Object


Numbers are essential in game development. They are used to keep track of score, how far an enemy is from the player, and how many lives the player has left, etc…
To simply create a variable with a number you would declare it like the example below:

var score = 100;           // A number without decimals
var playerLocation = 20.10; // A number with decimals


Strings can be considered as a sequence of characters. These can be used to display helpful information on the HUD or dialogue within the game.   Take the score for example.

It would be helpful if there was text in front of the score number within a game to make it clear where the score number is located on the HUD.
To declare a string in JavaScript it is very similar to how to declare a number, but it’s surrounded by quotation marks:

var scoreString = "Score:";


The Boolean primitive can only have the values true or false besides for an exception.   This is very useful when trying to detect if a player has been it by a projectile or another NPC.
Booleans declaration examples:

var isPlayerHit = false;
var playerHasAmmo = true;

There are some rules to the Boolean that should be kept in mind:

  •  False Is when the variable is 0, empty, undefined, NaN, null, or undefined.
  •  If it’s not on the list above, then everything else is considered true.

Here are a few more examples of how booleans would work:

var ammo = 0;               // false
var scoreString = “Score:”; // true
var ammoCount = 123;        // true
var playerName = “”;        // false

It’s very important to understand these rules, because it could cause some unexpected results when testing, and sometimes they will be hard to find and fix!


After going through this tutorial there may be one question that will come to mind.  Why is there a semicolon after every line of code?  JavaScript does not require them to be there since it has automatic insertion, however it is used for best practice.

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1 Comment on "Javascript Variables And DataTypes"

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shamsuddeen abdulkadir
shamsuddeen abdulkadir

This is cool. more of them pls

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