Conditional Statements (if, else if, else)

Every program eventually needs to do different things depending on a value. JavaScript uses if, else if, and else for this — with curly braces marking each block, unlike Python's indentation.

let age = 20;
if (age >= 18) {
  console.log("You are an adult");
} else {
  console.log("You are a minor");
}

You are an adult

=== vs. ==

JavaScript has two equality operators, and the difference genuinely matters: === checks value and type together (strict equality), while == converts types before comparing (loose equality), which can produce surprising results.

console.log(5 === 5);
console.log(5 === "5");
console.log(5 == "5");

true
false
true

Always use === unless you have a specific reason not to. == quietly converts "5" and 5 to be equal, which is rarely what you actually intended, and is a common source of subtle bugs.

Chaining conditions with else if

let score = 75;
if (score >= 90) {
  console.log("A");
} else if (score >= 80) {
  console.log("B");
} else if (score >= 70) {
  console.log("C");
} else {
  console.log("F");
}

C

JavaScript checks each condition top to bottom and stops at the first one that's true — score >= 70 matches before it ever reaches else, so "C" is printed and everything after is skipped.

Next: for loops — repeating code over every item in a collection.