Variable Definition

• A variable is like a box in programming.

• It has a unique name that helps describe its contents.

• The name that assign to a variable should be easy to remember and understand the purpose of the variable.

Variable Creation in JavaScript

• In JavaScript, there are three ways to declare variables: var, let, and const.

• var was traditionally used, but let and const offer more predictable scoping behavior.

Declaration with var, let, and const

• var: Declares a variable globally or locally to a function, and it can be reassigned.

• let: Introduces block-scoping, allowing a variable to be limited to the block, statement, or expression where it is defined. It can be reassigned.

• const: Also block-scoped, but it cannot be reassigned after initialization. It is typically used for values that should not be changed.

Assignment Operation

• The equal sign (=) is used as an assignment operator.

• It indicates that whatever is on the right side of the equal sign will be stored in the variable on the left side.

Storing Data

• Variables can store various types of data.

• In the provided example, a string of characters (a string) is stored in the variable.

Primary Data Types in JavaScript

#	Data Type
1	Undefined	Default value when a variable is declared but not assigned.
2	Null	Represents the intentional absence of any object value.
3	Boolean	Represents logical values true or false.
4	Number	Represents numeric values, including both integers and floating-point numbers.
5	BigInt	Represents whole numbers of any size, allowing for precise handling of very large integers
6	String	Represents textual data, enclosed in single or double quotes.
7	Symbol	Represents unique and immutable values to create completely unique identifiers
8	Object	Represents a collection of key-value pairs.

Difference between undefined and null

	Undefined	Null
Definition	A variable has been declared but has not yet been assigned a value.	An assignment value representing no value.
Origin	An ECMAScript (ES1) feature.	A primitive value in JavaScript.
Syntax	Does not have any specific syntax. It can be assigned to a variable, but it is not typically done intentionally.	null
Type	Not a global property.	A global property.
Assignment	Can be unintentionally assigned by declaring a variable without assigning a value.	Explicitly assigned to a variable to represent the absence of value.

Undefined Vs Null in JavaScript

Boolean Values in JavaScript

In JavaScript, the following values evaluate to false in a boolean context:

• false

• null

• undefined

• 0

• -0

• NaN

• An empty string ('')

Example Scenario

#	Data Type	Example
1	Undefined	let myVariable;
2	Null	let myVariable = null;
3	Boolean	let isTrue = true;
4	Number	let myNumber = 42;
5	BigInt	let bigInteger = 1234567890123456789012345678901234567890n;
6	String	let myString = "Hello, World!";
7	Symbol	const uniqueSymbol = Symbol('uniqueKey');
8	Object	let myObject = { key: 'value' };

Conclusion

• Variables, declared with var, let, or const, allow programmers to store and manage data effectively in a program.

• They act as containers with unique names, making it easier to work with and understand the code.