What does "? :" mean?

Question

I have a generic JS question that I'm not even sure how to put it.

In what cases do you use the following code structure? What does it mean (or use does this have)? And what is this practice called?

x1 = x2 ? x3 : x4;

Can you give references, examples and possibilities please?

It's called the [ternary operator](http://en.wikipedia.org/wiki/Ternary_operation). It is a shorthand if-else. It is used in many high-level programming languages. — Mr. Polywhirl, Apr 09 '14 at 11:14
@henser—it's *a* [ternary operator](http://en.wikipedia.org/wiki/%3F:), but in ECMAScript it's called the [*conditional operator*](http://ecma-international.org/ecma-262/5.1/#sec-11.12). — RobG, Apr 09 '14 at 11:17
Got it. Thank you all and sorry for possible duplicate. This is not an easy one to search for without any reference. — henser, Apr 09 '14 at 11:25

score 0 · Answer 1 · answered Apr 09 '14 at 11:15

0

the following thing

  if(x>10)
  {
      y=10;
  }
  else
  {
      y=9;
  }

can be written as

  (x>10) ? y=10 : y=9;

I think now you understood

answered Apr 09 '14 at 11:15

King of kings

697
2
6
21

1

This really doesn't compare because you're doing the assignment inside the ternary operation. – David Apr 09 '14 at 11:17
what about this "var val=(x>10) ? 10 : 9;" – King of kings Apr 09 '14 at 11:20
That is closer, except you still have an obvious logical thing going on, but nonetheless. – David Apr 09 '14 at 12:25

score 0 · Answer 2 · answered Apr 09 '14 at 11:16

0

if x2 is false, x1 = x4 if x2 is true, x1 = x3

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator

answered Apr 09 '14 at 11:16

user1021605

221
3
14

score 0 · Answer 3 · answered Apr 09 '14 at 11:16

0

In expanded code this says:

if(x2){
    x1 = x3;
}
else{
    x1 = x4
}

If you're familiar with the ternary operator (if not, look it up) then this might make a lot more sense.

x1 = (x2 ? x3 : x4);

answered Apr 09 '14 at 11:16

David

4,249
5
27
56

score 0 · Answer 4 · edited Nov 16 '15 at 23:57

0

It's called the ternary operator. It is a shorthand of if-else. It is used in many high-level programming languages.

x1 = x2 ? x3 : x4;

the above code can be expanded to:

x1 = undefined;

if (x2) {
    x1 = x3;
} else {
    x1 = x4;
}

edited Nov 16 '15 at 23:57

henser

3,181
2
33
44

answered Apr 09 '14 at 11:18

Mr. Polywhirl

31,606
11
65
114

score 0 · Answer 5 · answered Apr 09 '14 at 11:18

0

This is a ternary operator.

if X1 = X2 , X1 takes the value X3 else X1 takes the value X4.

answered Apr 09 '14 at 11:18

Deepu Sasidharan

4,763
8
32
84

score 0 · Answer 6 · answered Apr 09 '14 at 11:18

? : is a 'ternary operator'; it takes three arguments. The first argument is a test, the second argument is return value if test was true, and the third is a return value if the test was false.

so 1 === 1 ? 'foo' : 'bar' would return 'foo' and 1 === 0 ? 'foo' : 'bar' would return 'bar'. This can always be replaced with an if..else structure, but given its short form it can keep your code uncluttered.

If the test and return values are very complex in form, I would use the more "traditional" if..else structure.

What does "? :" mean?

6 Answers6