JS104 - Operators & Expressions

Operators allow you to perform calculations, compare values, and build logic in your JavaScript programs.
An expression is any piece of code that produces a value.

Arithmetic Operators

Arithmetic operators are used for basic mathematical operations.

let a = 10;
let b = 3;
 
a + b;   // 13
a - b;   // 7
a * b;   // 30
a / b;   // 3.333...
a % b;  // 1 (remainder)
a ** b; // 1000 (exponent)

Assignment Operators

let x = 5;
x += 3; // 8
x -= 2; // 6
x *= 2; // 12

Shorter syntax makes code easier to maintain.

Comparison Operators

Used to compare two values.

5 > 3;   // true
5 < 3;   // false
5 >= 5;  // true
5 <= 4;  // false

Equality

5 == "5"   // true (loose equality)
5 === "5" // false (strict equality)

Always prefer strict equality (===).

Inequality

10 !== 10 // false
10 !== 5  // true

Logical Operators

Used for combining conditions.

true && true   // true
true && false  // false
true || false  // true
false || false // false
!true           // false

Logical operators are essential for conditional logic.

String Operators

let first = "Hello";
let second = "World";
 
first + " " + second; // "Hello World"

Expressions in JavaScript

An expression produces a value.

Examples:

2 + 2
"JS" + "101"
isLoggedIn && hasToken

All of these generate a result and can be assigned to variables.

Operator Precedence

Some operators run before others.
Multiplication happens before addition.

2 + 3 * 4 // 14 (not 20)

Use parentheses to control execution order:

(2 + 3) * 4 // 20

Summary

In this lesson, you learned:

• Arithmetic operators
• Assignment operators
• Comparison and equality operators
• Logical operators
• String concatenation
• How expressions produce values
• Operator precedence

Next, we will introduce control flow and learn how JavaScript makes decisions using if, else, switch and the ternary operator.