Variables are a fundamental concept in many computer languages and knowing how to work with them is essential knowledge.
This tutorial focuses on:
- What is a variable?
- Declaring variables
- Naming variables
- Printing variables
What is a variable?
A variable is a container which stores information in a computer's memory. The value of a variable can change all throughout a script.
In the above example, a variable named aNumber is declared. You can assign a value to a variable at the same time that it is declared. This process is known as initialization.
NOTE: The var keyword should be used only once with each variable - during declaration. After a variable has been declared or initialized, you can refer to it by its name without the var keyword.
When naming variables, several rules should be followed:
- Make sure that the variable name is descriptive - If you do not give a variable a descriptive name, it will be hard to understand what the variable refers to. For example, if you wanted to create a variable which would hold a value signifying the amount of chairs in a room, which variable name would be more appropriate - numChairs or a? The better choice for the variable name would be numChairs because it is more descriptive.
- Make sure the variable name is of appropriate length - Make sure the variable name is long enough to be descriptive, but not too long.
- Do not use special symbols in variable names such as !@#%^&* - As is the rules with spaces, special symbols are not allowed in variable names. Using special symbols in variable names will generate an error. There is however one special symbol that can be used in variable names, and that symbol is the undersocre ( _ ) symbol. Variable names can only contain letters, numbers and the underscore ( _ ) symbol.
- Be careful about the first character of a variables name - The first character of a variables name must be a letter or an underscore. If the first character of a variable name is not a letter or an underscore, an error will be generated!
Variables are printed by including the variable name in a document.write() command. When printing the value of a variable, the variable name should NOT be included in double quotes.
You can also print variables together with regular text. To do this, use the + symbol to join the text and variable values together.