What is "?:" notation in JavaScript?

Question

I found this snippet of code in my travels in researching JSON:

var array = typeof objArray != 'object' ? JSON.parse(objArray) : objArray;

I'm seeing more and more of the ? and : notation. I don't even know what it is called to look it up! Can anyone point me to a good resource for this? (btw, I know what != means).

Solution 1

It's called a Conditional (ternary) Operator. It's essentially a condensed if-else.

So this:

var array = typeof objArray != 'object' ? JSON.parse(objArray) : objArray;

...is the same as this:

var array;
if (typeof objArray != 'object') {
    array = JSON.parse(objArray);
} else {
    array = objArray;
}

Solution 2

It's the ternary conditional operator -- basically,

if (condition) {
   a = 4;
}
else {
   a = 5;
}

becomes

a = condition ? 4 : 5;

Solution 3

That’s called the conditional operator:

condition ? expr1 : expr2

If condition is true, the operator returns the value of expr1; otherwise, it returns the value of expr2.

Solution 4

Just read it like this:

result = (condition) ? (true value) : (false value);

place what ever you like in the 3 operators.

As many has compared it to an IF.. THEN structure, so it is.

View more solutions

Comments

[Razor Storm]

Actually it is CALLED a conditional operator, but it IS A ternary operator. A ternary operator is any operation that takes 3 inputs. In many contexts, however, ternary operator has become synonymous with conditional since the conditional is either the most famous or sometimes the only ternary operator present in that language. For example, ++ -- are called unary operators, and + - / are called binary operators, etc. But that's just semantics, good answer, plus 1. :)

[Marcel Korpel]

@Razor – Nice addition; also have a look at the ECMAScript 5 specification of the Conditional Operator ( ? : ).

[Peter Ajtai]

Like Razor pointer out in the accepted answer: It's actually the JS conditional operator, which is the only ternary operator in JS.

[Peter Ajtai]

+1 for naming the only ternary operator in Javascript correctly.

[Peter Ajtai]

@Razor - +1 for your comment, and according to the MDC the conditional operator is the only ternary operator in Javascript.