Lesson 1 of 5 · 15–25 minutes

Conditions

🏠The everyday picture

"If it's raining, take an umbrella; otherwise, wear sunglasses." Every day we choose based on a condition. Programs do the same.

📘What it really is

if runs code only when a condition is true; else runs when it isn't:

const age = 17;
if (age >= 18) {
  console.log("You can register.");
} else {
  console.log("Please ask a parent to register for you.");
}

else if checks more conditions in order. The first true one wins, and the rest are skipped:

if (score >= 80) {
  grade = "Distinction";
} else if (score >= 60) {
  grade = "Pass";
} else {
  grade = "Try again";
}

Combine conditions with && and || (Module 17).
Truthy and falsy: in a condition, 0, "" (empty text), null, undefined and NaN count as false; almost everything else counts as true. So if (name) means "if a name was given".
The ternary is a one-line if: const label = isOpen ? "Open" : "Closed";.
The curly braces { } mark which lines belong to the condition. Indentation makes it readable.

🖱️Try it

In main.js, write code that takes a number of modules done (0 to 100) and prints which level the learner is on: modules 1–10 are Level 1, 11–20 Level 2, and anything above 20 "Level 3 or above". Test with 0, 5, 15 and 40.

✅Quick check

In an if / else if / else chain, a value matches two conditions. Which code runs?

Show the answer

Only the first matching one. The rest are skipped.

What does if (email) check?

Show the answer

Whether email has a truthy value, so not empty, null or undefined.