Variables are used in JavaScript, as they are in many other programming languages. Variable refers to something that can change. Variables in JavaScript can be declared using the keywords const, var, or let.
Variables are simply data storage containers.
You will be learning why Javascript variables are used, how you can use them as well as the differences between var, const, and let.
You need to understand basic rules for declaring a variable in Javascript. A lot of time, you need to follow these rules strictly. The rules are:
- The variable names must always begin with a letter (a-z or A-Z), dollar ($) symbol, or underscore ( )
- We can put numbers (0 to 9) after the initial letter.
- Variables in JavaScript are case-sensitive, meaning you must be very observant when adding these variables. This means; y and Y are totally different.
Starting With Javascript Variables
Data is raw information that we utilize in computer programs during coding. Your Instagram username, for example, is a raw piece of data.
A large portion of programming is concerned with modifying or presenting data. To accomplish so, programmers require a method of storing and tracking data. Let me provide an example to show this.
We’ll start by launching our JS console. Use the shortcut Ctrl + Shift + J on Linux and Windows to open your JS console in the Chrome browser. In contrast, you can use Command + Option + J on a Macbook.
After launching the console, think of a random number and input it into the console. For this article, I’ll be using the number Eight (8).
What if we need to refer back to that random number? We’ll have to enter it a second time. That’s why we need a mechanism to refer to this raw data so that we may use it all through our software.
Introducing Javascript Variables
Thinking of variables as tags for our values is a good comparison. Consider a Peanut jar with the word “Peanuts” on it. The variable, Peanuts, in this case, points to a value, which is the Peanuts themselves.
Let’s define a variable, age, then we assign our random number (value), 8, to it using the assignment operator. We’ll employ the “var” keyword.
var age = 8
Variables are used by programmers to provide a name to a variable so that it may be reused, updated, or simply kept track of. Any JavaScript type can be stored in variables.
We may refer to this number later now that we have assigned it to the variable age. If you now put the variable age into your console, you will get the number 4 back. It’s like a shortcut to that number “Eight.”
Javascript Variable Scope
A variable’s scope defines the part of your program where it is specified and defined. Variables in JavaScript have just two scopes.
- Global variables have global scope, meaning they may be declared anywhere in your lines of JavaScript code.
- Local Variables, on the other hand, are only accessible within the function in which it is declared. Function parameters always have to be function-specific.
A local variable having the same name takes priority over a global variable having the same name in the body of a function. When you define a local variable having the exact name as a global variable, the global variable is essentially hidden. Consider the following illustration:
<html>
<body onload = checkscope();>
<script type = "text/javascript">
<!--
var myVar = "global"; // Declare a global variable
function checkscope( ) {
var myVar = "local"; // Declare a local variable
document.write(myVar);
}
//-->
</script>
</body>
</html>
Declaring Multiple Variables
These can be specified on the same line, split with a comma.
var one = 1, two = 'two', three;
Words That Cannot Be Used as Variables in Javascript
- abstract
- boolean
- break
- byte
- case
- catch
- char
- class
- const
- continue
- debugger
- default
- delete
- do
- double
- enum
- export
- extends
- false
- final
- finally
- float
- for
- function
- goto
- if
- instanceof
- implements
- import
- in
- int
- interface
- long
- native
- new
- null
- package
- private
- protected
- public
- return
- short
- static
- super
- switch
- synchronized
- this
- throw
- throws
- transient
- true
- try
- typeof
- var
- void
- volatile
- while
- with
