Question mark and colon in JavaScript

Question

I came across the following line

hsb.s = max != 0 ? 255 * delta / max : 0;

What do the ? and : mean in this conte

Answer 1

? : isn't this the ternary operator?

var x= expression ? true:false

Answer 2

Be careful with this. A -1 evaluates to true although -1 != true and -1 != false. Trust me, I've seen it happen.

so

-1 ? "true side" : "false side"

evaluates to "true side"

Answer 3

It is called the Conditional Operator (which is a ternary operator).

It has the form of: condition ? value-if-true : value-if-false
Think of the ? as "then" and : as "else".

Your code is equivalent to

if (max != 0)
  hsb.s = 255 * delta / max;
else
  hsb.s = 0;

Answer 4

?: is a short-hand condition for else {} and if(){} problems. So your code is interchangeable to this:

if(max != 0){
       hsb.s = 225 * delta / max
}
else {
       hsb.s = 0
}

MDN - Conditional (Ternary) Operator

Answer 5

Properly parenthesized for clarity, it is

hsb.s = (max != 0) ? (255 * delta / max) : 0;

meaning return either

• 255*delta/max if max != 0
• 0 if max == 0

Answer 6

This is probably a bit clearer when written with brackets as follows:

hsb.s = (max != 0) ? (255 * delta / max) : 0;

What it does is evaluate the part in the first brackets. If the result is true then the part after the ? and before the : is returned. If it is false, then what follows the : is returned.