JavaScript

What is JavaScript Syntax?

JavaScript syntax refers to the rules and structure of how JavaScript code should be written and interpreted by the browser. If you don’t follow these rules, the JavaScript engine will throw errors.

---

1️⃣ JavaScript Case Sensitivity

JavaScript is case-sensitive, meaning myVar and myvar are treated as different variables.

🔹 Example:

let name = "Alice";  
let Name = "Bob";  

console.log(name);  // Output: Alice  
console.log(Name);  // Output: Bob  

---

2️⃣ JavaScript Statements

A JavaScript program consists of statements, which are instructions executed by the browser one by one.

🔹 Example:

let a = 10;  
let b = 20;  
let sum = a + b;  
console.log(sum);  // Output: 30  

✔️ Each statement ends with a semicolon (;) (optional but recommended).
✔️ JavaScript ignores extra spaces and line breaks.

---

3️⃣ JavaScript Variables (Declaration & Assignment)

Variables are used to store data in JavaScript.

🔹 Declaring Variables:

let x = 5;  // Using let  
const y = 10;  // Using const (value cannot change)  
var z = 15;  // Using var (old method, avoid using it)  

🔹 Rules for Naming Variables:
✅ Must start with a letter, _, or $
✅ Cannot start with a number (e.g., 1name ❌)
✅ JavaScript keywords cannot be used as variable names (e.g., let let = 5; ❌)

---

4️⃣ JavaScript Data Types

JavaScript has different types of data that variables can hold.

🔹 Example:

let name = "John";  // String  
let age = 25;  // Number  
let isStudent = true;  // Boolean  
let fruits = ["Apple", "Banana", "Mango"];  // Array  
let person = { firstName: "John", lastName: "Doe" };  // Object  
let value = null;  // Null  
let undefinedValue;  // Undefined  

---

5️⃣ JavaScript Operators

Operators perform operations on variables and values.

Arithmetic Operators

Used for basic math operations.

let sum = 10 + 5;   // Addition (+)  
let diff = 10 - 5;  // Subtraction (-)  
let prod = 10 * 5;  // Multiplication (*)  
let div = 10 / 5;   // Division (/)  
let mod = 10 % 3;   // Modulus (%)  
let power = 2 ** 3; // Exponentiation (2³ = 8)  

Comparison Operators

Used for comparing values.

console.log(10 > 5);  // true  
console.log(10 < 5);  // false  
console.log(10 == "10");  // true (loose comparison)  
console.log(10 === "10"); // false (strict comparison)  

Logical Operators

Used to combine conditions.

console.log(true && false);  // false (AND)  
console.log(true || false);  // true (OR)  
console.log(!true);  // false (NOT)  

---

6️⃣ JavaScript Comments

Comments are used to make code more readable.

🔹 Single-line comment:

// This is a single-line comment  
console.log("Hello, JavaScript!");  

🔹 Multi-line comment:

/*  
   This is a  
   multi-line comment  
*/  
console.log("Hello, World!");  

---

7️⃣ JavaScript Conditional Statements (If-Else, Switch)

Used to make decisions in code.

🔹 If-Else Statement:

let age = 18;  
if (age >= 18) {  
    console.log("You are an adult.");  
} else {  
    console.log("You are a minor.");  
}

🔹 Switch Statement:

let fruit = "apple";  
switch (fruit) {  
    case "banana":  
        console.log("You selected a banana.");  
        break;  
    case "apple":  
        console.log("You selected an apple.");  
        break;  
    default:  
        console.log("Invalid choice.");  
}

---

8️⃣ JavaScript Loops (For, While, Do-While)

Used to repeat a block of code multiple times.

🔹 For Loop:

for (let i = 1; i <= 5; i++) {  
    console.log("Count: " + i);  
}

🔹 While Loop:

let num = 1;  
while (num <= 5) {  
    console.log("Number: " + num);  
    num++;  
}

🔹 Do-While Loop (Runs at least once):

let count = 1;  
do {  
    console.log("Count: " + count);  
    count++;  
} while (count <= 5);

---

9️⃣ JavaScript Functions

Functions are used to create reusable blocks of code.

🔹 Function Declaration:

function greet(name) {  
    return "Hello, " + name + "!";  
}
console.log(greet("Alice"));  

🔹 Arrow Function (ES6+):

const greet = (name) => "Hello, " + name + "!";  
console.log(greet("Bob"));

---

🔟 JavaScript Objects

Objects store key-value pairs.

🔹 Example:

let person = {  
    firstName: "John",  
    lastName: "Doe",  
    age: 30,  
    greet: function() {  
        return "Hello, " + this.firstName;  
    }  
};  

console.log(person.greet());  // Output: Hello, John  

---

💡 JavaScript Syntax Summary

Concept	Syntax	Example
Variables	let, const, var	let name = "Alice";
Data Types	String, Number, Boolean, Object, Array	let x = 10;
Operators	Arithmetic, Comparison, Logical	x > 5
Comments	// (Single-line), /* */ (Multi-line)	// This is a comment
If-Else	if (condition) {}	if (x > 10) {}
Loops	for, while, do-while	for (let i = 0; i < 5; i++) {}
Functions	function name() {}	function greet() { return "Hi!"; }
Objects	{ key: value }	let obj = {name: "Alice"};

---

🚀 Conclusion

• JavaScript syntax defines how to write and execute code correctly.
• Follow proper rules for variables, operators, conditions, loops, and functions.
• Writing clean and structured code makes JavaScript easier to read and debug.