JavaScript Booleans

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

Boolean Values

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

YES / NOON / OFFTRUE / FALSE

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

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

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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:

OperatorDescriptionExample==equal toif (day == "Monday")>greater thanif (salary > 9000)<less thanif (age < 18)

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

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

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

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

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

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

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The Boolean value of undefined is false:

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

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The Boolean value of null is false:

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

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

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

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The Boolean value of NaN is false:

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

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Booleans Can be Objects

Normally JavaScript booleans are primitive values created from literals: var x = false

But booleans can also be defined as objects with the keyword new: var y = new Boolean(false)

Example

var x = false;
var y = new Boolean(false);

// typeof x returns boolean
// typeof y returns object

Try it yourself »

Do not create Boolean objects. It slows down execution speed.
The new keyword complicates the code. This can produce some unexpected results:

When using the == operator, equal booleans are equal:

Example

var x = false;            
var y = new Boolean(false);

// (x == y) is true because x and y have equal values

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When using the === operator, equal booleans are not equal, because the === operator expects equality in both type and value.

Example

var x = false;            
var y = new Boolean(false);

// (x === y) is false because x and y have different types

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Or even worse. Objects cannot be compared:

Example

var x = new Boolean(false);            
var y = new Boolean(false);

// (x == y) is false because objects cannot be compared

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Note the difference between (x==y) and (x===y).
Comparing two JavaScript objects will always return false.

Complete Boolean Reference

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

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

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