Operators

Theory

Operators are symbols that perform operations on values (operands). JavaScript provides a rich set of operators for various tasks.

Arithmetic operators handle mathematical calculations:

• + (addition), - (subtraction), * (multiplication), / (division), % (modulus/remainder), ** (exponentiation)

The + operator also performs string concatenation when one operand is a string. The % operator returns the remainder of division, useful for checking even/odd numbers or cycling through ranges.

Assignment operators assign values to variables. The basic = assigns a value. Compound assignment operators combine arithmetic with assignment:

• +=, -=, *=, /=, %=, **=

let x = 10;
x += 5; // x = x + 5 → 15
x *= 2; // x = x * 2 → 30

Comparison operators compare values and return a boolean:

• == (loose equality — coerces types)
• === (strict equality — no coercion)
• != (loose inequality), !== (strict inequality)
• >, <, >=, <=

Always prefer === over == to avoid unexpected type coercion results. For example, 0 == false is true but 0 === false is false.

Logical operators work with boolean values:

• && (AND) — returns true if both operands are truthy
• || (OR) — returns true if either operand is truthy
• ! (NOT) — inverts the boolean value

Logical operators use short-circuit evaluation. With &&, if the first operand is falsy, the second is never evaluated. With ||, if the first operand is truthy, the second is skipped.

The ternary operator (condition ? expr1 : expr2) is a concise alternative to if/else for simple conditions.

The nullish coalescing operator (??) returns the right operand only when the left operand is null or undefined. Unlike ||, it does not treat 0, '', or false as falsy.

let username = null;
let displayName = username ?? "Guest"; // "Guest"

Optional chaining (?.) safely accesses nested properties without throwing an error if an intermediate value is null or undefined.

Operator precedence determines the order in which operators are evaluated. Multiplication and division have higher precedence than addition and subtraction. Use parentheses () to override precedence and make expressions clearer.

Practical Examples

Exercises

const celsius = 30;\n// Calculate fahrenheit and print status

86°F - Hot

const username = 'john_doe';\nconst password = 'secret123';\n// Your validation logic here

Access Granted

let total = 0;\nconst item1 = 25.99;\nconst item2 = 89.99;\nconst coupon = null;\n// Calculate total with discount if applicable

Total: $115.98\nDiscounted: $104.38

Mini Quiz

Mini Project