JavaScript Booleans

A JavaScript Boolean represents one of two values: true or false.

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Boolean Values

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

• YES / NO
• ON / OFF
• TRUE / FALSE

For this, JavaScript has a Boolean data type. It can only take the values true or false.

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The Boolean() Function

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

Example

Boolean(10 > 9)        // returns true

Or even easier:

Example

(10 > 9)              // also returns true 10 > 9                // also returns true

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Comparisons and Conditions

The chapter JS Comparisons gives a full overview of comparison operators.

The chapter JS Conditions gives a full overview of conditional statements.

Here are some examples:

Operator	Description	Example
==	equal to	if (day == "Monday")
>	greater than	if (salary > 9000)
<	less than	if (age < 18)

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

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Everything With a "Real" Value is True

Examples

100

3.14

-15

"Hello"

"false"

7 + 1 + 3.14

5 < 6

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Everything Without a "Real" is False

The Boolean value of 0 (zero) is false:

var x = 0;
Boolean(x);       // returns false

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

var x = -0;
Boolean(x);       // returns false

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

var x = "";
Boolean(x);       // returns false

The Boolean value of undefined is false:

var x;
Boolean(x);       // returns false

The Boolean value of null is false:

var x = null;
Boolean(x);       // returns false

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

var x = false;
Boolean(x);       // returns false

The Boolean value of NaN is false:

var x = 10 / "H";
Boolean(x);       // returns false

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Boolean Properties and Methods

Primitive values, like true and false, cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.