JavaScript Basics

JavaScript Advanced

JavaScript Arrays

JavaScript Functions

JavaScript Objects

JavaScript DOM

JavaScript String

How to use Logical operators in JavaScript?

In JavaScript, there are three logical operators:

Logical AND
Logical OR
Logical NOT

Note: Logical AND and Logical OR are binary operators, whereas logical NOT is a unary operator.

Logical AND operator

Logical AND operator is represented by the double ampersand (&&). It returns true if both operands are true. If one or both operands is false, then it returns false.

let result = x && y;

The following truth table shows the result produced by the logical AND operator when applied to the boolean operands.

operand1	operand2	operand1 && operand2
true	true	true
true	false	false
false	true	false
false	false	false

Let's see how to use logical AND operator with the help of an example:

let x = true,
    y = false;
 
console.log(x && y); //false

Note: To know logical AND operator in detail, visit How to use Logical AND operator in JavaScript?

Logical OR operator

The double pipe (||) is used to represent Logical OR operator. It returns true if one or both operands is true. If both operands are false, then it returns false.

let result = x || y;

The following truth table displays the result produced by the logical OR operator when applied to the boolean operands.

operand1	operand2	operand1 \|\| operand2
true	true	true
true	false	true
false	true	true
false	false	false

The following example explains the working of logical OR operator:

let x = true,
    y = false;
 
console.log(x || y); //true

Note: To learn about logical OR operator in detail, visit How to use Logical OR operator in JavaScript?

Logical NOT operator

In JavaScript, logical NOT is represented by an exclamation point (!).

Logical NOT operator is written before an operand. It returns true if an operand is a falsy value. If an operand is a truthy value, then it returns false.

The following code shows how to use logical NOT in JavaScript:

!x

In JavaScript, the following are considered falsy values.

null
undefined
NaN
0
-0
"" (empty string)

These six values work as a false value. Apart from the falsy values, all other values are truthy values. For example, objects, arrays, etc. are truthy values

The following table shows the result produced by the logical NOT operator when applied to different JavaScript values.

x	Logical NOT (!x)
true	false
false	true
undefined	true
null	true
"" is empty string	true
0	true
any number other than 0	false
NaN	true
object	false
array	false

The following example shows how to use logical NOT operator:

let x = 123;
console.log(!x); //false
x = 0;
console.log(!x); //true
x = [1, 2, 3];
console.log(!x); //false