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JavaScript - Conditional Operators

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JavaScript Conditional Operators

The conditional operator in JavaScript first evaluates an expression for a true or false value and then executes one of the two given statements depending upon the result of the evaluation. The conditional operator is also known as the ternary operator.

The JavaScript conditional (ternary) operator is only operator that takes three operands – a condition followed by a question mark (?), then the first expression to be executed if the condition is truthy followed by a colon (:), and finally the second expression to be executed if the condition is falsy.

There are six falsy values in JavaScript. These are − 0 (zero), false, empty string ('' or ""), null, undefined, and NaN. All other values are treated as truthy in JavaScript.

Syntax

Following is the syntax of conditional (ternary) operator in JavaScript −

var variable = condition ? exp1 : exp2;

Parameters

Here, we have explained the parameters in the above statement.

  • condition − It is a conditional statement.
  • exp1 − If the conditional statement evaluates truthy, control flow executes the exp1 expression.
  • exp2 − If the conditional statement evaluates falsy, control flow executes the exp2 expression.

If the value of the condition is any falsy value, the result of the expression will be the value of exp2; otherwise, it will be the value of exp1.

Example

In the example below, we compare the value of the num1 and num2 variables in the conditional statement. Here, the conditional statement evaluates true, so the result variable contains the value of the first expression. 

<html>
<body>
<div id="output"></div>
<script>
   var num1 = 90;
   var num2 = 67;
   var res = num1 > num2 ? "num1 is greater than num2" : "num2 is greater than num1";
   document.getElementById("output").innerHTML = res;
</script>
</body>
</html>

It will produce the following result − 

num1 is greater than num2

Example

In the example below, we assign the value to the object property according to the conditional statement’s result.

Now, imagine what if you need to write the if-else statement to assign value to each property conditionally. The code will become complex, but with the ternary operator, you can easily do it with a single line of code.

<html>
<body>
<div id="output"></div>
<script>
   const year = 2004;
   const obj = {
	  name: "John",
	  age: year < 2005 ? "adult" : "minor",
	  city: "New York"
   };

   document.getElementById("output").innerHTML = 
   obj.name + " is " + obj.age + " and lives in " + obj.city;
</script>
</body>
</html>

It will produce the following result −

John is adult and lives in New York

Example

This example demonstrates that you can also use the expression instead of values. According to the conditional statement, control flow evaluates the first or second expression and assigns the resultant value to the 'result' variable.

<html>
<body>
<div id="output"></div>
<script>
   let operator = '-';
   let res = operator == '+' ? 10 + 20 : 10 - 20;
   document.getElementById("output").innerHTML = "The result is: " + res;
</script>
</body>
</html>

It will produce the following result −

The result is: -10

In short, you can use the ternary or conditional operator to shorten the code, which uses the if-else statement.

Handling null values

We can use the JavaScript conational operator to handle null value to set a default value if the user passes a null value.

Example

Try the following example −

<html>
<body>
<div id="output"></div>
<script>
   const greet = (user) => {
      const name = user? user.name : "stranger";
      return `Hello, ${name}`;
   };
   document.getElementById("output").innerHTML =
   greet({ name: "John" }) + "<br>" +
   greet(null);
</script>
</body>
</html>

It will produce the following result −

Hello, John
Hello, stranger
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