JavaScript Basics

In this section, we’ll cover the fundamental building blocks of JavaScript. Understanding these concepts will lay a solid foundation for everything you’ll learn later. This includes variables, data types, operators, and control structures, all of which are essential in creating any JavaScript program.

Variables

Variables are used to store information that can be referenced and manipulated in your code. JavaScript allows you to declare variables using three keywords: var, let, and const.

var: The original way to declare variables in JavaScript. It is function-scoped, which can lead to issues in block-scoped environments. It’s generally recommended to use let or const instead.
let: Introduced in ES6, let allows you to declare variables that are block-scoped, meaning their values can be updated but are only accessible within the block in which they are defined.
const: Also introduced in ES6, const is used to declare variables whose values cannot be changed once assigned. This is ideal for constants.

Examples:

var name = "Alice";
let age = 25;
const country = "USA";

// Updating variables
age = 26; // This works since `let` allows updates
// country = "Canada"; // This would throw an error since `const` does not allow reassignment

Data Types

JavaScript has several data types, which can be classified into two categories: primitive and object.

Primitive Data Types

String: Textual data, enclosed in quotes.
```
let greeting = "Hello, World!";
```
Number: Numeric values, including both integers and floating-point numbers.
```
let score = 95.5;
```
Boolean: Represents a logical entity, either true or false.
```
let isActive = true;
```
Undefined: A variable that has been declared but has not been assigned a value.
```
let value;
console.log(value); // undefined
```
Null: Represents the intentional absence of any value.
```
let data = null;
```
Symbol: A unique and immutable primitive value, often used for object property keys.
```
let symbol = Symbol("unique");
```
BigInt: Allows the representation of numbers larger than what the Number type can handle.
```
let bigNumber = 1234567890123456789012345678901234567890n;
```

Objects

Objects are collections of key-value pairs and can represent more complex data.

Example

let person = {
  name: "Alice",
  age: 25,
  isStudent: false,
};

Basic Operators

Operators are symbols that perform operations on variables and values. They can be classified into different types.

Arithmetic Operators

+: Addition
-: Subtraction
*: Multiplication
/: Division
%: Modulus (remainder)
**: Exponentiation

Example

let sum = 5 + 3; // 8
let product = 4 * 2; // 8
let remainder = 10 % 3; // 1

Assignment Operators

=: Assigns a value
+=: Adds and assigns
-=: Subtracts and assigns

Example

let a = 10;
a += 5; // a = 15
a -= 3; // a = 12

Comparison Operators

These operators compare two values and return a Boolean (true or false).

==: Equal to (converts types if necessary)
===: Strict equal to (no type conversion)
!=: Not equal to
!==: Strict not equal to
>: Greater than
<: Less than

Example

console.log(5 == "5"); // true (loose equality)
console.log(5 === "5"); // false (strict equality)

Logical Operators

&&: Logical AND
||: Logical OR
!: Logical NOT

Example

let isAdult = true;
let hasPermission = false;
console.log(isAdult && hasPermission); // false
console.log(isAdult || hasPermission); // true
console.log(!isAdult); // false

Control Structures

Control structures allow you to control the flow of the program based on conditions.

`if`, `else`, and `else if` Statements

Used to execute blocks of code based on certain conditions.

Example

let temperature = 30;

if (temperature > 35) {
  console.log("It's too hot!");
} else if (temperature > 25) {
  console.log("It's warm.");
} else {
  console.log("It's cold.");
}

`switch` Statement

The switch statement is used when you have multiple possible values for a variable and want to execute different code for each value.

Example

let day = 3;
let dayName;

switch (day) {
  case 1:
    dayName = "Monday";
    break;
  case 2:
    dayName = "Tuesday";
    break;
  case 3:
    dayName = "Wednesday";
    break;
  default:
    dayName = "Invalid day";
}

console.log(dayName); // "Wednesday"

Summary

In this section, you’ve learned the basics of JavaScript, including how to declare and use variables, understand different data types, use basic operators for computations, and control the flow of your program with conditional statements. Mastering these fundamentals is crucial before moving on to more advanced topics such as functions and object-oriented programming.

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