JAVASCRIPT Variables
JAVASCRIPT
Variables in JavaScript can be considered as containers for data.
JavaScript variables
➔ JavaScript variables are used to store the value of any data or information.
➔ The variable should have a unique name within the scope of the variable called identifier.
JavaScript variables naming Conventions:
➔ Naming a variable requires following a standard naming convention for identifiers.
➔ The identifier name must start with a letter, underscore (_), or dollar sign ($).
➔ The characters following the first character of the identifier name can be any combination of numbers, letters, underscores, or dollar signs.
➔ Identifier names are case sensitive, so the uppercase and lowercase letters of the name are important.
JavaScript variable data type:
➔ JavaScript is a dynamically typed language, meaning that the data type of a variable is determined at runtime.
➔ Therefore, programmers do not have to specify the data type when declaring variables.
➔ A variable in JavaScript can hold information of the following data types, which are determined at runtime execution time.
Number: For integer and decimal data types.
String: For string or character data types.
Boolean: For logical values like true or false.
Object: For object type data like arrays.
Null: Deliberately maintaining the absence of a value.
Undefined: The default value of a variable when it has no value assigned to it.
Keywords for Declaration in JavaScript
| Keyword | Scope | Reassignment | Redeclaration | Description |
|---|---|---|---|---|
| let | Block-scoped | Allowed | Not allowed | The standard and recommended way to declare a variable whose value may change. |
| const | Block-scoped | Not allowed | Not allowed | The standard and recommended way to declare a constant type variable whose value cannot be changed after initialisation. |
| var | Function-scoped | Allowed | Allowed (in non-strict mode) | This is an outdated method of variable declaration and is not recommended in modern JavaScript due to potential scripting and extraction issues |
Syntax
/* modern approach to declare a variable. */
let a = 20;
/* modern approach to declare a constant. */
const b = 30;
/* older method to declare a variable. not recommended */
var c = 10
JavaScript variables
Example
<!DOCTYPE html>
<html>
<head>
<title>JavaScript variable Example</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta charset="utf-8">
</head>
<body>
<h3>JavaScript variable Example</h3>
<script>
/* modern approach to declare a variable. */
let a = 20;
/* modern approach to declare a constant. */
const b = 30;
/* older method to declare a variable. not recommended */
var c = 10
console.log(a);
console.log(b);
console.log(c);
</script>
</body>
</html>
Click on the "Try it Now" button to see how it works.
JavaScript variable name
Example
<!DOCTYPE html>
<html>
<head>
<title>JavaScript variable name example</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta charset="utf-8">
</head>
<body>
<h3>JavaScript variable name example</h3>
<script>
/* The dentifier has underscore in its name. */
let student_id = 50;
/* The dentifier has dollar in its name. */
let student$age = 22;
/* The dentifier has underscore and digit in its name. */
let st_address1 = "Road-05, House-06";
console.log(student_id);
console.log(student$age);
console.log(st_address1);
</script>
</body>
</html>
Click on the "Try it Now" button to see how it works.
JavaScript dynamic variable type.
Example
<!DOCTYPE html>
<html>
<head>
<title>JavaScript variable type example</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta charset="utf-8">
</head>
<body>
<h3>JavaScript variable type example</h3>
<script>
/* variable number type */
let id = 50;
/* variable string type */
let name = "Maria";
/* variable boolear type */
let eligible = true;
/* variable undefined type */
let email;
/* variable null type */
let address = null;
/* variable array type */
let skills = ["HTML", "CSS", "JS"];
</script>
</body>
</html>
Click on the "Try it Now" button to see how it works.