Variables and Data Types

Variables are used to store data in JavaScript. They can be declared using the var, let, or const keywords.

 
var age = 25; // Using var
let name = "John"; // Using let
const PI = 3.14159; // Using const

 

JavaScript has several data types, including:

  • Number: Represents both integers and floating-point numbers.
  • String: Represents textual data enclosed in single or double quotes.
  • Boolean: Represents a logical value, either true or false.
  • Undefined: Represents an uninitialized variable or a non-existent object property.
  • Null: Represents an intentionally empty value.
  • Object: A collection of key-value pairs, capable of storing complex data structures.
  • Symbol: A new data type introduced in ES6, used to create unique identifiers.

Operators

JavaScript supports various operators for performing calculations, comparisons, and other operations:

  • Arithmetic Operators: +, -, *, /, %, ++, --
  • Assignment Operators: =, +=, -=, *=, /=, %=
  • Comparison Operators: ==, ===, !=, !==, >, <, >=, <=
  • Logical Operators: &&, ||, !
  • Bitwise Operators: &, |, ^, ~, <<, >>, >>>

Statements and Expressions

Statements are the basic units of execution in JavaScript. They can be separated by semicolons or written on separate lines. Expressions are a combination of values, variables, operators, and function calls that produce a value.

 
let x = 5; // Statement
let y = x + 3; // Expression
 

Comments

Comments are used to add explanatory notes or temporarily disable code in JavaScript. There are two types of comments:

  • Single-line comments: Preceded by // 
    // This is a single-line comment
  • Multi-line comments: Enclosed between /* and */ 
    /* This is
		   a multi-line
		   comment */

In the next chapter, we'll explore control flow statements and loops, which are essential for creating dynamic and interactive programs.