JavaScript Booleans

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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)        // 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.

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
»
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
»
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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