Conditional logic using if...then statements

├─ index.html
└─ script.js

An if statement runs code only when something is true.

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

The condition goes in round brackets. The code goes in curly braces.

Branching

if (a) {
	// when a is true
} else if (b) {
	// when a is false and b is true
} else {
	// when neither is
}

JavaScript checks the branches top to bottom and stops at the first true one, so the order you write them in changes the result.

Truthy and falsy

Anything can be used as a condition. These six count as false:

false, 0, "" (empty string), null, undefined, NaN

Everything else counts as true ~ including "0", "false" and an empty array, all of which have confused people at three in the morning.

This is why you often see:

if (name) {
	// runs when name has any content at all
}

The ternary

const label = hour < 12 ? "AM" : "PM";

Condition, ?, value-if-true, :, value-if-false. Perfect for choosing between two values. Please don’t nest them ~ I’ve read that code and I didn’t enjoy it.