sqrt(-1) is broken. What happened?

Question

I'm trying to let i be the square root of -1 (sqrt(-1)). It is a defined value:

i = sqrt(-1)

var i = sqrt(-1);
fill(0, 0, 0);
text(i, 25, 25);

It gives me an error. What happened?

Answer 1

sqrt() is a function that already has a defined behavior. From MDN:

The square root of the given number. If the number is negative, NaN is returned.

NaN is not an error in itself. It's a value that means "not a number" - you can find more information here.

You seem to be thinking about functions and values in a different direction than I would. Looking at this line:

var i = sqrt(-1);

This line isn't saying "define the square root of -1 to be equal to i". It's saying: create a variable named i, and set its value equal to whatever is returned by calling sqrt(-1).

So the code calls sqrt(-1), which returns NaN, so the value of i is NaN. Then when you try to use that value, you'll see NaN.