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

What is the ?: (question mark and colon operator aka. conditional or "ternary") operator and h开发者_C百科ow can I use it?

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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:

var userType;
if (userIsYoungerThan18) {
  userType = "Minor";
} else {
  userType = "Adult";
}

if (userIsYoungerThan21) {
  serveDrink("Grape Juice");
} else {
  serveDrink("Wine");
}

This can be shortened with the ?: like so:

var userType = userIsYoungerThan18 ? "Minor" : "Adult";

serveDrink(userIsYoungerThan21 ? "Grape Juice" : "Wine");

Like all expressions, the conditional operator can also be used as a standalone statement with side-effects, though this is unusual outside of minification:

userIsYoungerThan21 ? serveGrapeJuice() : serveWine();

They can even be chained:

serveDrink(userIsYoungerThan4 ? 'Milk' : userIsYoungerThan21 ? 'Grape Juice' : 'Wine');

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;

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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.

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I want to add some to the given answers.

In case you encounter (or want to use) a ternary in a situation like 'display a variable if it's set, else...', you can make it even shorter, without a ternary.

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Instead of:

var welcomeMessage  = 'Hello ' + (username ? username : 'guest');

You can use:

var welcomeMessage  = 'Hello ' + (username || 'guest');

This is Javascripts equivallent of PHP's shorthand ternary operator ?:

Or even:

var welcomeMessage  = 'Hello ' + (username || something || maybethis || 'guest');

It evaluates the variable, and if it's false or unset, it goes on to the next.

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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

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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: Mozilla Developer Center'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;
}

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Most of the answers are correct but I want to add little more. The ternary operator is right-associative, which means it can be chained in the following way if … else-if … else-if … else :

function example() {
    return condition1 ? value1
         : condition2 ? value2
         : condition3 ? value3
         : value4;
}

Equivalent to:

function example() {
    if (condition1) { return value1; }
    else if (condition2) { return value2; }
    else if (condition3) { return value3; }
    else { return value4; }
}

More details is here

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z = (x == y ? 1 : 2);

is equivalent to

if (x == y)
    z = 1;
else
    z = 2;

except, of course, it's shorter.

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Ternary Operator

Commonly we have conditional statements in Javascript.

Example:

if (true) {
    console.log(1)
} 
else {
    console.log(0)
}
# Answer
# 1

but it contain two or more lines and cannot assign to a variable. Javascript have a solution for this Problem Ternary Operator. Ternary Operator can write in one line and assign to a variable.

Example:

var operator = true ? 1 : 0
console.log(operator)
# Answer
# 1

This Ternary operator is Similar in C programming language.

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Hey mate just remember js works by evaluating to either true or false, right?

let's take a ternary operator :

questionAnswered ? "Awesome!" : "damn" ;

First, js checks whether questionAnswered is true or false.

if true ( ? ) you will get "Awesome!"

else ( : ) you will get "damn";

Hope this helps friend :)

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It is called the ternary operator

tmp = (foo==1 ? true : false);

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Ternary expressions are very useful in JS, especially React. Here's a simplified answer to the many good, detailed ones provided.

condition ? expressionIfTrue : expressionIfFalse

Think of expressionIfTrue as the OG if statement rendering true;
think of expressionIfFalse as the else statement.

Example:

var x = 1;
(x == 1) ? y=x : y=z;

this checked the value of x, the first y=(value) returned if true, the second return after the colon : returned y=(value) if false.

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x = 9
y = 8

unary

++x
--x

Binary

z = x + y

Ternary

2>3 ? true : false;
2<3 ? true : false;
2<3 ? "2 is lesser than 3" : "2 is greater than 3";

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It's an if statement all on one line.

So

var x=1;
(x == 1) ? y="true" : y="false";
alert(y);

The expression to be evaluated is in the ( )

If it matches true, execute the code after the ?

If it matches false, execute the code after the :

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The conditional (ternary) operator is the only JavaScript operator that takes three operands. This operator is frequently used as a shortcut for the if statement.

condition ? expr1 : expr2 

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

function fact(n) {
  if (n > 1) {
    return n * fact(n-1);
  } else {
    return 1;
  }
  // we can replace the above code in a single line of code as below
  //return (n != 1) ? n * fact(n - 1) : 1;
}
console.log(fact(5));

For more clarification please read MDN document link

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This is probably not exactly the most elegant way to do this. But for someone who is not familiar with ternary operators, this could prove useful. My personal preference is to do 1-liner fallbacks instead of condition-blocks.

  // var firstName = 'John'; // Undefined
  var lastName = 'Doe';

  // if lastName or firstName is undefined, false, null or empty => fallback to empty string
  lastName = lastName || '';
  firstName = firstName || '';

  var displayName = '';

  // if lastName (or firstName) is undefined, false, null or empty
  // displayName equals 'John' OR 'Doe'

  // if lastName and firstName are not empty
  // a space is inserted between the names
  displayName = (!lastName || !firstName) ? firstName + lastName : firstName + ' ' + lastName;


  // if display name is undefined, false, null or empty => fallback to 'Unnamed'
  displayName = displayName || 'Unnamed';

  console.log(displayName);

Ternary Operator

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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>

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Ternary operator is just a simple way to write if else condition. It is widely used in ReactJS.

For Example:

const x = 'foo';

// Instead of if else use this
x === 'foo' ? alert('True') : alert('False');

// Output
// alert box will prompt 'True'

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By using Ternary operator, write a program to Print “Even Number”, if the number is even or Print “Odd Number”, if the number is odd.

let a = 13;
let b = a%2!==0 ? "is Odd number" : "is Even number";
// let b = a%2==0 ? "is Even number" : "is Odd number";
console.log(a+" "+b);

Output : 13 is Odd number

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It's called the ternary operator. For some more info, here's another question I answered regarding this:

How to write an IF else statement without 'else'

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If you have one condition check instance function in javascript. it's easy to use ternary operator. which will only need one single line to implement. Ex:

    private module : string ='';
    private page:boolean = false;
    async mounted(){
     if(this.module=== 'Main')
    {
    this.page = true;}
    else{
    this.page = false;
    }
}

a function like this with one condition can be written as follow.

this.page = this.module=== 'Main' ?true:false;

condition ? if True : if False

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 (sunday == 'True') ? sun="<span class='label label-success'>S</span>" : sun="<span class='label label-danger'>S</span>";

 sun = "<span class='label " + ((sunday === 'True' ? 'label-success' : 'label-danger') + "'>S</span>"