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JS TutorialLesson #21

JavaScript Booleans

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

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:

Description	Example	Returns
Equal to	(x == 8)	false
Not equal to	(x != 8)	true
Greater than	(x > 8)	false
Less than

(x See Also: > JavaScript Comparisons

Conditions

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

Example	Result
if (day == "Monday")	true or false
if (salary > 9000)	true or false

| if (age See Also: > JavaScript if > JavaScript if else

Loops

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

Description	Example
For loop

for (i = 0; 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

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Boolean(10 > 9)

Or even easier:

Example

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(10 > 9)

Everything With a "Value" is True

Examples

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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

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0 is false

"" is false

undefined is false

null is false

NaN is false

false is false

Example

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let x = 0;

Boolean(x);

Example

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let x = -0;

Boolean(x);

Example

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let x = "";

Boolean(x);

Example

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let x;

Boolean(x);

Example

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let x = null;

Boolean(x);

Example

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let x = false;

Boolean(x);

Example

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let x = 10 / "Hallo";

Boolean(x);