JavaScript If/Else

The if statement runs a block of code only when a condition is true. It’s the most basic form of decision-making in code.

const age = 21;

if (age >= 18) {
  console.log("You're an adult.");
}

else — the fallback

Use else for what to do when the condition is false.

const hour = 14;

if (hour < 12) {
  console.log("Good morning!");
} else {
  console.log("Good afternoon!");
}

else if — multiple conditions

Stack else if for more than two options.

const score = 78;

if (score >= 90) {
  console.log("A");
} else if (score >= 80) {
  console.log("B");
} else if (score >= 70) {
  console.log("C");
} else if (score >= 60) {
  console.log("D");
} else {
  console.log("F");
}
// "C"

JavaScript checks each condition top to bottom and runs the first one that’s true. Order matters.

Truthy Conditions

The condition doesn’t have to be a comparison — any value works. JavaScript converts it to a boolean. (Refresher: the eight falsy values are false, 0, -0, 0n, "", null, undefined, NaN.)

const name = "Ada";

if (name) {
  console.log(`Hello, ${name}!`);
} else {
  console.log("No name provided.");
}

This is a common idiom for “if the variable has a meaningful value.”

A Classic Mistake: = vs ===

= is assignment, not comparison. Mixing them up is a famous bug.

const age = 21;

// BUG: assignment, not comparison
// if (age = 18) { … }
// This would assign 18 to age (impossible with const — TypeError).
// With let, the condition becomes "is 18 truthy?" which is always true.

// CORRECT:
if (age === 18) {
  console.log("Just became an adult.");
}

Skipping the Braces

For a single statement, you can drop the { }. Most teams require them anyway — they avoid bugs when someone later adds a second line.

// Legal:
if (loggedIn) showDashboard();

// Preferred:
if (loggedIn) {
  showDashboard();
}

Try It Yourself

const total = 120;
// your code here

const total = 120;
let finalPrice;
if (total > 100) {
  finalPrice = total * 0.9;
} else {
  finalPrice = total;
}
console.log(finalPrice);

Up Next

For a quick yes/no choice between two values, JavaScript has a compact form — the ternary operator.