Which one is on

Challenge 15 of 16

Two lamps side by side and one question between them, so exactly one of them is lit at any time. That is the else all over again: two outcomes, and no way to get both or neither.

Choose the colour each lamp takes when it is the one that is off.

Your code JavaScript

Choose the colour each lamp takes when it is the one that is off.

Console print() output

0 / 30 frames · 400×400

Target

Yours

Yours over Target — ghosted shapes are in the target but missing from yours

Results

Press Run to check your code

Penalties: none this run

Report this challenge

Lesson Or Else

An if on its own can only say what to do when the answer is true. When it is false, nothing happens — and a badge that stayed grey because nothing happened is a strange thing to have to explain.

else is the other half.

if (score > 100) {
shapeColour(GREEN);
} else {
shapeColour(RED);
}

Read it as one sentence: if score is over 100 use green, or else use red. The else has no question of its own. It does not need one, because it means everything the if did not catch.

Exactly one of those two blocks runs. Never both, never neither. That is worth saying plainly, because it is what makes an else so restful to read: whatever happens, you know something happened.

Notice what you no longer need. In the last topic every badge had a grey pen picked up first, in case the if did not run. With an else naming a colour on each side there is nothing for a fallback to cover, so it can go.

Either side can hold as many lines as it likes, and they need not do the same kind of thing:

if (score > 200) {
howBig = 260;
} else {
howBig = 100;
}

A colour, a size, a place, a whole background, even a different shape altogether. The one rule is that the else comes straight after the if's closing curly bracket, on the same line as it in these challenges.

Two questions written one after another are two separate decisions. Ask the same thing twice with the colours swapped over and you get two lamps, exactly one of which is lit.

So far every question has been the same one: is this bigger than that. The next topic has the rest of them.