Question mark and colon in JavaScript

Question mark and colon in JavaScript

I came across the following line
hsb.s = max != 0 ? 255 * delta / max : 0;

What do the ? and : mean in this context?

Solutions/Answers:

Solution 1:

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;

Solution 2:

Properly parenthesized for clarity, it is

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

meaning return either

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

Solution 3:

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.

Related:  Functions that return a function

Solution 4:

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

? is a ternary operator, it works like an if in conjunction with the :

!= means not equals

So, the long form of this line would be

if (max != 0) { //if max is not zero
  hsb.s = 255 * delta / max;
} else {
  hsb.s = 0;
}

Solution 5:

? : isn’t this the ternary operator?

var x= expression ? true:false

Solution 6:

?: 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