Conditional Operator

Summary

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

Operator
Implemented in: JavaScript 1.0
ECMA Version: ECMA-262

Syntax

condition ? expr1 : expr2

Parameters

condition
An expression that evaluates to true or false.
expr1, expr2
Expressions with values of any type.

Description

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:

document.write ("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 hadRelations = false,
  isSure = false,
  presidentQuote = hadRelations ? "Had relations" : isSure ? "Did not have relations" : "I admit";
  
console.log( presidentQuote ); // Prints "I admit" in the console

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

var bStop = false, nAge = 16;

nAge > 18 ? location.assign("continue.html") : bStop = true;

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

var bStop = false, nAge = 23;

nAge > 18 ? (
    alert("Ok, you can go."),
    location.assign("continue.html")
) : (
    bStop = 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 nAge = 16;

var sURL = nAge > 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 nAge > 18
) : (
    alert("You are much too young!"),
    alert("Sorry :-("),
    // etc. etc.
    "stop.html" // the value to be assigned if !(nAge > 18)
);

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

Document Tags and Contributors

Last updated by: Havvy,