JavaScript Booleans

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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 / NO
ON / OFF
TRUE / 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)

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Or even easier:

Example

(10 > 9)
10 > 9

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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 basis for all JavaScript comparisons and conditions.

Everything With a "Value" is True

Examples

100

3.14

-15

"Hello"

"false"

7 + 1 + 3.14

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Everything Without a "Value" is False

The Boolean value of 0 (zero) is false:

let x = 0;
Boolean(x);

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

let x = -0;
Boolean(x);

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

let x = "";
Boolean(x);

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The Boolean value of undefined is false:

let x;
Boolean(x);

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The Boolean value of null is false:

let x = null;
Boolean(x);

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

let x = false;
Boolean(x);

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The Boolean value of NaN is false:

let x = 10 / "Hallo";
Boolean(x);

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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

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Do not create Boolean objects.

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

Boolean objects can produce unexpected results:

When using the == operator, x and y are equal:

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

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When using the === operator, x and y are not equal:

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

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Note the difference between (x==y) and (x===y).

(x == y) true or false?

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

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(x === y) true or false?

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

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Comparing two JavaScript objects 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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