How do you use the ? : (conditional) operator in J

Question

Can someone please explain to me in simple words what is the ?: (conditional, "ternary") operator and how to use it?

Answer 1

We can use with Jquery as well as length as below example :

Suppose we have GuarantorName textbox which has value and want to get firstname and lastname- it may be null. So rathar than

        var gnamesplit = $("#txtGuarantorName").val().split(" ");
        var gLastName = "";
        var gFirstName = "";
        if(gnamesplit.length > 0 ){
           gLastName  = gnamesplit[0];        
        }
        if(gnamesplit.length > 1 ){
           gFirstName = gnamesplit[1];        
        }

We can use below code with Jquery with minimum code

    

    var gnamesplit = $("#txtGuarantorName").val().split(" ");
    var gLastName = gnamesplit.length > 0  ? gnamesplit[0] : "";
    var gFirstName =  gnamesplit.length > 1  ? gnamesplit[1] : "";
    $("#txtLastName").val(gLastName);
    $("#txtFirstName").val(gFirstName);
    
    

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<div >
  Guarantor Name: <input type="text" id="txtGuarantorName" value="ASP.NET Core"  /><br/>
  <br/>
  <br/>
  
  First Name: <input type="text" id="txtLastName" value="ASP.NET Core"  />
  Last Name: <input type="text" id="txtFirstName" value="ASP.NET Core"  />
</div>

Answer 2

This is a one-line shorthand for an if-else statement. It's called the conditional operator.¹

Here is an example of code that could be shortened with the conditional operator:

if(userIsYoungerThan21) {
  serveGrapeJuice();
}
else {
  serveWine();
}

This can be shortened with the ?: like so:

userIsYoungerThan21 ? serveGrapeJuice() : serveWine();

In Javascript conditional operator can evaluate to an expression, not just a statement:

var userType = userIsYoungerThan18 ? "Minor" : "Adult";
serveDrink(userIsYoungerThan21 ? "Grape Juice" : "Wine");

They can even be chained:

userIsYoungerThan4 ? serveMilk() : userIsYoungerThan21 ? serveGrapeJuice() : serveWine();

Be careful, though, or you will end up with convoluted code like this:

var k = a ? (b ? (c ? d : e) : (d ? e : f)) : f ? (g ? h : i) : j;

---

¹ Often called "the ternary operator," but in fact it's just a ternary operator [an operator accepting three operands]. It's the only one JavaScript currently has, though.

Answer 3

It's called the 'ternary' or 'conditional' operator.

Example

The ?: operator can be used as a shortcut for an if...else statement. It is typically used as part of a larger expression where an if...else statement would be awkward. For example:

var now = new Date();
var greeting = "Good" + ((now.getHours() > 17) ? " evening." : " day.");

The example creates a string containing "Good evening." if it is after 6pm. The equivalent code using an if...else statement would look as follows:

var now = new Date();
var greeting = "Good";
if (now.getHours() > 17)
   greeting += " evening.";
else
   greeting += " day.";

From MSDN JS documentation.

Basically it's a shorthand conditional statement.

Also see:

• Operator precedence with Javascript Ternary operator
• Wikipedia

Answer 4

It's a little hard to google when all you have are symbols ;) The terms to use are "javascript conditional operator".

If you see any more funny symbols in Javascript, you should try looking up Javascript's operators first: MDC's list of operators. The one exception you're likely to encounter is the $ symbol.

To answer your question, conditional operators replace simple if statements. An example is best:

var insurancePremium = age > 21 ? 100 : 200;

Instead of:

var insurancePremium;

if (age > 21) {
    insurancePremium = 100;
} else {
    insurancePremium = 200;
}