Conditional (ternary) Operator

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.

SyntaxEDIT

condition ? expr1 : expr2 

Parameters

condition

An expression that evaluates to true or false.

expr1, expr2

Expressions with values of any type.

DescriptionEDIT

If condition is true, the operator returns the value of expr1; otherwise, it returns the value of expr2. For example, to display a different message based on the value of the isMember variable, you could use this statement:

'The fee is ' + (isMember ? '$2.00' : '$10.00');

You can also assign variables depending on a ternary result:

var elvisLives = Math.PI > 4 ? 'Yep' : 'Nope';

Multiple ternary evaluations are also possible (note: the conditional operator is right associative):

var firstCheck = false,
    secondCheck = false,
    access = firstCheck ? 'Access denied' : secondCheck ? 'Access denied' : 'Access granted';
  
console.log(access); // logs "Access granted"

You can also use ternary evaluations in free space in order to do different operations:

var stop = false, age = 16;

age > 18 ? location.assign('continue.html') : stop = true;

You can also do more than one single operation per case, separating them with a comma:

var stop = false, age = 23;

age > 18 ? (
    alert('OK, you can go.'),
    location.assign('continue.html')
) : (
    stop = true,
    alert('Sorry, you are much too young!')
);

You can also do more than one operation during the assignation of a value. In this case, the last comma-separated value of the parenthesis will be the value to be assigned.

var age = 16;

var url = age > 18 ? (
    alert('OK, you can go.'), 
    // alert returns "undefined", but it will be ignored because
    // isn't the last comma-separated value of the parenthesis
    'continue.html' // the value to be assigned if age > 18
) : (
    alert('You are much too young!'),
    alert('Sorry :-('),
    // etc. etc.
    'stop.html' // the value to be assigned if !(age > 18)
);

location.assign(url); // "stop.html"

SpecificationsEDIT

Specification	Status	Comment
ECMAScript 2017 Draft (ECMA-262) The definition of 'Conditional Operator' in that specification.	Draft
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Conditional Operator' in that specification.	Standard
ECMAScript 5.1 (ECMA-262) The definition of 'The conditional operator' in that specification.	Standard
ECMAScript 1st Edition (ECMA-262) The definition of 'The conditional operator' in that specification.	Standard	Initial definition. Implemented in JavaScript 1.0.