JavaScript Operators and Expressions

Working with Operators and Expressions

Operators allow you to perform operations on variables and values. JavaScript has several types of operators.

Arithmetic Operators

let a = 10;
let b = 3;

console.log(a + b);  // Addition: 13
console.log(a - b);  // Subtraction: 7
console.log(a * b);  // Multiplication: 30
console.log(a / b);  // Division: 3.333...
console.log(a % b);  // Modulus (remainder): 1
console.log(a ** b); // Exponentiation: 1000

Assignment Operators

let x = 5;
x += 3;  // Same as: x = x + 3 (now x is 8)
x -= 2;  // Same as: x = x - 2 (now x is 6)
x *= 2;  // Same as: x = x * 2 (now x is 12)
x /= 4;  // Same as: x = x / 4 (now x is 3)

Comparison Operators

let num1 = 5;
let num2 = "5";

console.log(num1 == num2);   // true (loose equality)
console.log(num1 === num2);  // false (strict equality)
console.log(num1 != num2);   // false
console.log(num1 !== num2);  // true
console.log(num1 > 3);       // true
console.log(num1 <= 5);      // true

Logical Operators

let isAdult = true;
let hasLicense = false;

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

String Operators

let firstName = "John";
let lastName = "Doe";
let fullName = firstName + " " + lastName;  // "John Doe"

// Template literals (modern approach)
let greeting = `Hello, ${fullName}!`;  // "Hello, John Doe!"

Increment and Decrement

let counter = 5;
counter++;     // Post-increment: counter becomes 6
++counter;     // Pre-increment: counter becomes 7
counter--;     // Post-decrement: counter becomes 6
--counter;     // Pre-decrement: counter becomes 5

Operator Precedence

JavaScript follows mathematical order of operations:

let result = 2 + 3 * 4;        // 14 (not 20)
let result2 = (2 + 3) * 4;     // 20 (parentheses first)

Practice Exercise

// Calculator practice
let price = 29.99;
let quantity = 3;
let taxRate = 0.08;

let subtotal = price * quantity;
let tax = subtotal * taxRate;
let total = subtotal + tax;

console.log(`Price per item: $${price}`);
console.log(`Quantity: ${quantity}`);
console.log(`Subtotal: $${subtotal.toFixed(2)}`);
console.log(`Tax: $${tax.toFixed(2)}`);
console.log(`Total: $${total.toFixed(2)}`);

// Check if total is over $100
let isExpensive = total > 100;
console.log(`Is expensive? ${isExpensive}`);