Whta is JavaScript Booleans?
In JavaScript, Booleans represent one of two values: true or false. They are essential in programming because they drive decision-making and logic. Booleans are commonly used in conditional statements, loops and comparisons to control the flow of a program.
Boolean Values in JavaScript
A Boolean has only two possible values:
- true (truthy)
- false (falsy)
Example:
let isJavaScriptFun = true;
let isRainy = false;
console.log(isJavaScriptFun); // Output: true
console.log(isRainy); // Output: false
Boolean Conversion
JavaScript can automatically convert values to Booleans using truthy and falsy concepts.
Truthy Values
Values that are considered true in Boolean context:
- Non-empty strings (“Hello”)
- Non-zero numbers (
42, -1) - Objects (
{}) and Arrays ([ ]) - The Boolean true itself
Falsy Values
Values that are considered false in Boolean context:
- 0
- null
- undefined
- NaN (Not-a-Number)
- Empty string (“”)
- The Boolean false
Example:
console.log(Boolean(0)); // Output: false
console.log(Boolean("Hello")); // Output: true
console.log(Boolean(null)); // Output: false
console.log(Boolean([])); // Output: true
Boolean Comparison Operators
Comparison operators return Boolean values (true or false) based on conditions.
1. Equality Operators
- == (Loose equality): Compares values after type conversion.
- === (Strict equality): Compares both value and type.
Example:
console.log(5 == "5"); // Output: true (loose equality)
console.log(5 === "5"); // Output: false (strict equality)
2. Inequality Operators
- != (Loose inequality): Checks if values are not equal after type conversion.
- !== (Strict inequality): Checks if values and types are not equal.
Example:
console.log(10 != "10"); // Output: false
console.log(10 !== "10"); // Output: true
3. Comparison Operators
- < (less than)
- > (greater than)
- <= (less than or equal to)
- >= (greater than or equal to)
Example:
console.log(10 > 5); // Output: true
console.log(10 <= 5); // Output: false
Boolean Logical Operators
Logical operators are used to combine or modify Boolean expressions:
1. AND (&&)
Returns true if all conditions are true.
Example:
let age = 25;
let hasLicense = true;
console.log(age > 18 && hasLicense); // Output: true
2. OR (||)
Returns true if at least one condition is true.
Example:
let isWeekend = false;
let isHoliday = true;
console.log(isWeekend || isHoliday); // Output: true
3. NOT ( ! )
Reverses the Boolean value.
Example:
let isRaining = true;
console.log(!isRaining); // Output: false
Using Booleans in Conditional Statements
Booleans are often used in if…else conditions to determine the flow of a program.
Example:
let hasPassword = true;
if (hasPassword) {
console.log("Access granted!");
} else {
console.log("Access denied!");
}
// Output: Access granted!
Booleans in Functions
Functions can return Boolean values to indicate a condition or success/failure.
Example:
function isEven(number) {
return number % 2 === 0;
}
console.log(isEven(4)); // Output: true
console.log(isEven(7)); // Output: false
Practical Example: Login System
Booleans are critical for validating user input.
Example:
function login(username, password) {
const validUsername = "admin";
const validPassword = "1234";
if (username === validUsername && password === validPassword) {
return true;
} else {
return false;
}
}
console.log(login("admin", "1234")); // Output: true
console.log(login("user", "abcd")); // Output: false