JS Operators

JavaScript Operators: Arithmetic, Comparison, Logical, and Nullish

JavaScript operators perform math, assign values, compare data, and combine boolean conditions. Knowing how operators interact and which ones run first helps you write bug-free expressions across real applications.

Essential Operator Groups

JavaScript groups operators by the kind of work they perform on values (called operands):

Logical operators short-circuit from left to right. When the left side of && is falsy, JavaScript skips evaluating the right side completely. The same shortcut applies when the left side of || is truthy.

Modern Fallback Operators: ?? vs ||

Use the nullish coalescing operator (??) when you want a fallback only for null or undefined. Unlike ||, ?? keeps valid falsy values such as 0, "", or false.

const userPort = 0;
const safePort = userPort ?? 8080;   // Keeps 0
const wrongPort = userPort || 8080;  // Falls back to 8080!

const isLoggedIn = true;
const isAdmin = false;
const badge = isLoggedIn && isAdmin ? "Admin Panel" : "Member View";

console.log({ safePort, wrongPort, badge });

Operator Precedence Basics

JavaScript evaluates * and / before + and -, and evaluates && before ||. Whenever an expression mixes multiple operators, wrap parts in parentheses (...) so intent stays crystal clear to every reader.

Common Mistakes to Avoid

• Using == instead of ===: Loose equality converts types behind the scenes ("5" == 5 is true), causing subtle bugs. Always use strict === and !==.
• Mixing up || and ??: Using count || 10 replaces 0 with 10. Use count ?? 10 for numeric defaults.
• Over-nesting ternary operators: Chaining three ? : operators on one line is hard to read; switch to if...else blocks instead.

Frequently Asked Questions

What is the difference between && and || in JavaScript?

&& returns the first falsy operand or the last operand if all are truthy. || returns the first truthy operand or the last operand if all are falsy.

What does the typeof operator return?

typeof is a unary operator that returns a lowercase string naming the operand's type, such as "number", "string", or "boolean".

What does the ternary operator do?

The ternary operator cond ? valA : valB evaluates cond and returns valA when truthy or valB when falsy.