Very often in programming we need a data type that can have only two values, and those two values
are true and false. That is why JavaScript has a Boolean
data type. With the Boolean() function we can determine whether an expression (or variable)
is true or not. JavaScript statements enable comparison and checking of values using various operators
(==, ===, >, <). With them, we can check value equality, compare numbers, and execute conditional statements
(if, else).
The result of every comparison is a Boolean value true or false. Typically,
JavaScript Boolean values are primitive values created from literals. Boolean values can also be
defined as objects with the new keyword, but the use of Boolean objects is
discouraged, as it can lead to unexpected results when comparing values.
| Item | Description | Syntax | Example |
|---|---|---|---|
| Boolean values | |||
| true | Logically true | true |
let x = true; |
| false | Logically false | false |
let x = false; |
| Boolean() | Converts a value to boolean | Boolean(value) |
Boolean(0); // false |
| Falsy values (return false) | |||
| false, 0, -0, 0n | Numeric zeros | Boolean(0) |
Boolean(0); // false |
| "" | Empty string | Boolean("") |
Boolean(""); // false |
| null, undefined, NaN | Empty or invalid values | Boolean(null) |
Boolean(null); // false |
| Truthy values (return true) | |||
| Anything else | Everything that is not falsy | Boolean(value) |
Boolean("0"); // true |
| {}, [] | Empty objects and arrays | Boolean({}) |
Boolean([]); // true |
| Logical operators | |||
| && | AND (both must be true) | a && b |
true && false; // false |
| || | OR (at least one must be true) | a || b |
true || false; // true |
| ! | NOT (reverses the value) | !a |
!true; // false |
| !! | Double NOT (converts to boolean) | !!a |
!!"hello"; // true |
| Comparison operators (return boolean) | |||
| ===, !== | Strict equal/not equal (type + value) | a === b |
5 === "5"; // false |
| ==, != | Equal/not equal (with type conversion) | a == b |
5 == "5"; // true |
| > , < , >= , <= | Size comparison | a > b |
10 > 5; // true |
| Boolean object methods | |||
| constructor | Returns the function that created the Boolean prototype. | obj.constructor |
▶ Code example |
| prototype | Allows adding properties and methods to the Boolean prototype. | Boolean.prototype |
▶ Code example |
| toString() | Converts a Boolean value to a string. | bool.toString() |
▶ Code example |
| valueOf() | Returns the primitive value. | bool.valueOf() |
▶ Code example |
