JavaScript Booleans
The Boolean Data Type
In JavaScript, a Boolean is a primitive data type that can only have one of two values:
true or false
The Boolean value of an expression is the basis for all JavaScript comparisons and conditions.
Key Boolean Characteristics
- true and false are boolean data types
- true and false are the only possible boolean values
- true and false must be written in lowercase
- true and false must be written without quotes
Boolean Use Cases
Very often, in programming, you will need a data type that can represent one of two values, like:
- yes or no
- on or off
- true or false
Boolean values are fundamental for logical operations and control flow in JavaScript programming.
Comparisons
All JavaScript comparison operators (like ==, !=, <, >) return true or false from the comparison.
Given that x = 5, the table below explains comparison:
| Description | Example | Returns |
|---|---|---|
| Equal to | (x == 8) | false |
| Not equal to | (x != 8) | true |
| Greater than | (x > 8) | false |
| Less than | (x < 8) | true |
See Also:
Conditions
Booleans are extensively used in if statements to determine the code blocks to execute based on the logic.
| Example | Result |
|---|---|
| if (day == "Monday") | true or false |
| if (salary > 9000) | true or false |
| if (age < 18) | true or false |
Example
if (hour < 18) {
greeting = "Good day";
} else {
greeting = "Good evening";
}
Try it Yourself »
Loops
Booleans are extensively used in loops to determine conditions for looping.
| Description | Example |
|---|---|
| For loop | for (i = 0; i < 5; i++) |
| While loop | while (i < 10) |
| For in loop | for (x in person) |
| For of loop | for (x of cars) |
See Also:
The Boolean() Function
You can use the Boolean() function to find out if an expression (or a variable) is
true:
Or even easier:
Everything With a "Value" is True
Examples
100 is true
3.14 is true
-15 is true
true is true
"Hello" is true
"false" is true
(7 + 1 + 3.14) is true
[ ] is true
{ } is true
Try it Yourself »
Note
In JavaScript, both an empty array [ ] and an empty object { } are truthy because they are objects.
All objects in JavaScript evaluate to true in a boolean context, regardless of their content.
Everything Without a "Value" is False
Examples
0 is false
"" is false
undefined is false
null is false
NaN is false
false is false
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
Try
it yourself »
Warning
Do not create Boolean objects.
The new keyword complicates the code and slows down execution speed.
Boolean objects can produce unexpected results:
Booleans and boolean objects cannot be safely compared:
let x = Boolean(false);
let y = new Boolean(false);
(x == y) returns true
(x === y) returns false
Try it Yourself »
Comparing two JavaScript objects always returns 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.
