How to Declare a Variable in JavaScript

Variables in JavaScript, as in any programming language, hold the numbers, strings, and other values used by a program. They are declared using the var command.

Things You'll Need

• JavaScript editor

Instructions

Declare a Variable in JavaScript

1. Choose a variable name which meets JavaScript guidelines. Variables names can contain only numbers, letters, or underscores, and must start with a letter or underscore. The are case-sensitive: the variable ABC is distinct from abc.

2. Find the best place to declare your variable. Variables declared outside of a function are available to all commands throughout the entire script, and are called "global" while variables exclusive to a specific function are "local", declared inside the function.

3. Declare the variable using the var command, as follows:
   var my_variable;

4. Add additional variables to the declaration for compactness:
   var one_var, two_var;

5. Specify an initial value for the variable by following it with an equal sign and the value:
   var zero=0;

Tips & Warnings

• Place global variables at the beginning of your scripts so that they're clearly defined and accessible to the commands that need them later on.

• Although JavaScript does not require variables to be declared, it is always best to do so. Otherwise, you may end up inadvertently using the wrong value of a variable.