Making Decisions: if / else

So far every line of your code has run. Conditionals let programs choose.

if / else if / else

const score = 87;

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

The conditions are checked top to bottom; the first truthy one wins and the rest are skipped. The final else catches everything the earlier branches missed.

Truthiness

Conditions do not need to be booleans — JavaScript converts them:

• Falsy: false, 0, "" (empty string), null, undefined, NaN
• Truthy: everything else — including "0", "false", and []

const name = ""; // falsy!

if (name) {
  console.log("Hello, " + name);
} else {
  console.log("Please enter your name");
}

This pattern — if the value exists, use it, otherwise handle the missing case — is everywhere in real code.

Nesting and combining

const age = 15;
const withAdult = true;

if (age >= 18 || withAdult) {
  console.log("You can enter");
} else {
  console.log("Sorry, adults only");
}

Prefer combining conditions with &&/|| over deep nesting — flat reads better.

What you learned

• if / else if / else: first matching branch wins
• Falsy values: false, 0, "", null, undefined, NaN
• Combine conditions with logical operators instead of nesting deeply

Next: doing things repeatedly — loops.