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 / 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

Try it Yourself »

Or even easier:

Example

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

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

Try it Yourself »


Everything Without a “Value” is False

The Boolean value of 0 (zero) is false:

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

Try it Yourself »

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

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

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.