View Categories

Javascript Booleans

1 min read

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

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

Everything Without a “Value” is False #

The Boolean value of 0 (zero) is false:

Everything Without a "Value" is False The Boolean value of 0 (zero) is 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

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

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.


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.

Powered by BetterDocs

Leave a Reply