How do you use the conditional operator in JavaScript

Question

In simple words, what is the ?: (conditional, "ternary") operator and how can I use it?

Answer 1

It is possible to express an if-else expression in one line. The conditional operator is what it is called. 

The conditional operator can be used to shorten the following code:

var userType;
if (userIsYoungerThan18) {
  userType = "Minor";
} else {
  userType = "Adult";
}

if (userIsYoungerThan21) {
  serveDrink("Grape Juice");
} else {
  serveDrink("Wine");
}

This can be shortened with the ?: like so:

var userType = userIsYoungerThan18 ? "Minor" : "Adult";

serveDrink(userIsYoungerThan21 ? "Grape Juice" : "Wine");