Operators & Expressions

What is an Operator?

An operator is a symbol that tells JavaScript to perform a specific mathematical, relational, or logical operation and produce a result. An expression is any valid piece of code that resolves to a value — often built with operators.

For example: 5 + 3 is an expression that uses the addition operator +.

Arithmetic Operators

Use these to perform math operations on numbers.

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

Assignment Operators

Assign values to variables, often combined with arithmetic.

• = Assigns a value
• += Adds and assigns: x += 5 is the same as x = x + 5
• -= Subtracts and assigns
• *= Multiplies and assigns
• /= Divides and assigns

Comparison Operators

Compare two values and return a boolean (true or false).

• == Equal (loose equality, does type coercion)
• === Strict equal (recommended)
• != Not equal (loose)
• !== Strict not equal (recommended)
• > Greater than
• < Less than
• >= Greater than or equal
• <= Less than or equal

Logical Operators

Combine multiple conditions or invert boolean values.

• && AND — true only if both are true
• || OR — true if at least one is true
• ! NOT — inverts the boolean value

Operator Precedence

Just like in math, operators have a precedence that determines the order in which they are evaluated. Multiplication and division happen before addition and subtraction.

let result = 5 + 3 * 2; // 11, not 16

Use parentheses () to make your intention clear and override precedence.

let result2 = (5 + 3) * 2; // 16

Common Mistakes

• Using = (assignment) instead of === (comparison) in conditionals
• Forgetting that + also concatenates strings: "5" + 3 = "53"
• Confusing && and || logic

Quick Quiz

Summary

• Arithmetic operators: + - * / % **
• Assignment operators: = += -= *= /=
• Comparison operators: === !== > < >= <=
• Logical operators: && || !
• Use === and !== for strict comparisons
• Use parentheses to control evaluation order