Creative Services Toolkit


Javascript Variables

Learn about variables in Javascript and how you can use them in your creative.


The purpose of this tutorial is to teach you how Javascript variables work, and to show how they can save you time when coding creative.

Why does it matter?

Javascript variables store data. As a result they are useful for setting states of an creative (expanded, collapsed etc), defining data like URLs, and storing values we might need later.


Javascript variables function as a container to store values. The most simple variable is a boolean, which is like a switch, either in the true or false position. Variables can also be a number or a string (text).

A Basic Example

  • We created a new variable by typing the keyword var.
  • We gave the variable a name so we can use it later, which is onSlide
  • Then we set the value of the variable equal to 1.

Variable Names

  • onSlide is our variable name.
  • Variable names must begin with a letter (can't start with a number)
  • Variable names can contain letters and numbers, and ARE case sensitive
    Example: onSlide and onslide are different variables
  • In Javascript some words are off limits (called Reserved Words), so they can't be variable names
    Example: function, url, var, switch, this
    For a larger list check out This Link

Setting the value of a variable

  • When you first define a variable you can set it's value or you can just define it and leave it blank (var onSlide;)
  • After you define it you can change it's value at anytime by typing the variable name and the value you want it to equal.
  • Notice that when we set the value to 2, we don't put the word var in front. var is only needed when we first define/create the variable.

Using the Current Value of a Variable

  • Above we are creating a console.log that will log into the browser console whatever the value of the variable currently is.
  • You can also use an if statement to ask if the value of the variable equals a certain value.
    NOTE: The === (3 equals signs) is how we ask if the variable is equal to 3 (It's a question)
    NOTE: The !== is how we ask if the variable is NOT equal to 3 (It's still a question)
    NOTE: onSlide = 3 (1 equals sign) is how we set the variable equal to 3

Manipulating the Current Value

  • The code above adds 1 to the onSlide variable. So if it was 2, it will now be 3. Both lines of code add 1 to the current value.

Undefined Variables

  • When you create a variable you don't have to define it's value. The code above creates a new variable but it's not equal to anything.
  • If you try to get the value of this variable the result will be "undefined"
  • Undefined variables can occur when you're dynamically assigning the value.
    Example: If you are trying to find thumbnails on the page you might do var thumbs = $(".thumbs"). If none exist the variable "thumbs" will be undefined.

How to check if a variable is defined

  • The code above creates an if statement that asks if the value of onSlide does not equal "undefined", which means it is defined/has a value.
  • The code //do something will only run if the value of the variable is defined.
  • This is important because an undefined variable can cause your javascript to break.

Real World Examples

Getting the Current Item Inside a Function (see the functions tutorial if needed)

Create a Timestamp/Random Number

Create a Timer

Setup Slider Options