JavaScript Booleans

The Boolean Data Type

In JavaScript, a Boolean is a primitive data type that can only have one of two values:

true or false

The Boolean value of an expression is the basis for all JavaScript comparisons and conditions.

Key Boolean Characteristics

• true and false are boolean data types
• true and false are the only possible boolean values
• true and false must be written in lowercase
• true and false must be written without quotes

Boolean Use Cases

Very often, in programming, you will need a data type that can represent one of two values, like:

• yes or no
• on or off
• true or false

Boolean values are fundamental for logical operations and control flow in JavaScript programming.

Comparisons

All JavaScript comparison operators (like ==, !=, <, > ) return true or false from the comparison.

Given that x = 5, the table below explains comparison:

Example

let x = 5;

(x == 8); // equals false

(x != 8); // equals true

See Also:

JavaScript Comparisons

Conditions

Booleans are extensively used in if statements to determine the code blocks to execute based on the logic.

Example

if (hour < 18) {

  greeting = "Good day";

} else {

  greeting = "Good evening";

}

See Also:

JavaScript if

JavaScript if else

Loops

Booleans are extensively used in loops to determine conditions for looping.

Example

while (i < 10) {

  text += i;

  i++;

}

See Also:

JavaScript Loops

The Boolean() Function

You can use the Boolean() function to find out if an expression (or a variable) is true:

Example

Boolean(10 > 9)

Or even easier:

Example

(10 > 9)

Everything With a "Value" is True

Examples

100 is true

3.14 is true

-15 is true

true is true

"Hello" is true

"false" is true

(7 + 1 + 3.14) is true

[ ] is true

{ } is true

Note

In JavaScript, both an empty array [ ] and an empty object { } are truthy because they are objects.

All objects in JavaScript evaluate to true in a boolean context, regardless of their content.

Everything Without a "Value" is False

Examples

0 is false

"" is false

undefined is false

null is false

NaN is false

false is false

The Boolean value of 0 (zero) is false:

let x = 0;

Boolean(x);

The Boolean value of -0 (minus zero) is false:

let x = -0;

Boolean(x);

The Boolean value of ""(empty string) is false:

let x = "";

Boolean(x);

The Boolean value of undefined is false:

let x;

Boolean(x);

The Boolean value of null is false:

let x = null;

Boolean(x);

The Boolean value of false is (you guessed it) false:

let x = false;

Boolean(x);

The Boolean value of NaN is false:

let x = 10 / "Hallo";

Boolean(x);

JavaScript Booleans as Objects

Normally JavaScript booleans are primitive values created from literals:

let x = false;

But booleans can also be defined as objects with the keyword new:

let y = new Boolean(false);

Example

let x = false;

let y = new Boolean(false);

 //
typeof x returns boolean

 //
typeof y returns object

Warning

Do not create Boolean objects.

The new keyword complicates the code and slows down execution speed.

Boolean objects can produce unexpected results:

Booleans and boolean objects cannot be safely compared:

let x = Boolean(false);

let y = new Boolean(false);

(x == y) returns true

(x === y) returns false

Comparing two JavaScript objects always returns false.

Complete Boolean Reference

For a complete reference, go to the Complete JavaScript Boolean Reference.

The reference contains descriptions and examples of all Boolean properties and methods.