JavaScript Booleans

In JavaScript, a Boolean is a data type that represents one of two possible values: `true` or `false`. Booleans are commonly used in conditional statements and logical operations.

1. Boolean Values

A Boolean value can either be `true` or `false`. These values are typically used to control the flow of code based on conditions.

- Declaring Boolean Variables

You can declare Boolean variables and assign them values directly:

// Boolean variable examples
let isTrue = true;
let isFalse = false;

console.log(isTrue);  // true
console.log(isFalse); // false

            

2. Boolean Conversion

You can convert other data types to Boolean values using the `Boolean()` function or by using double negation (`!!`).

- Using `Boolean()` Constructor

The `Boolean()` function converts any value to its corresponding Boolean value:

// Convert values to Boolean
console.log(Boolean(0));           // false
console.log(Boolean(1));           // true
console.log(Boolean("hello"));     // true
console.log(Boolean(""));          // false
console.log(Boolean(null));        // false
console.log(Boolean(undefined));   // false

            

- Using Double Negation

Double negation (`!!`) is a shorthand method for converting values to Boolean:

// Convert values to Boolean using double negation
console.log(!!0);           // false
console.log(!!1);           // true
console.log(!!"hello");     // true
console.log(!!"");          // false
console.log(!!null);        // false
console.log(!!undefined);   // false

            

3. Logical Operations

Booleans are frequently used in logical operations such as AND (`&&`), OR (`||`), and NOT (`!`).

- Logical AND (`&&`)

The logical AND operator returns `true` if both operands are true:

// Logical AND
console.log(true && true);  // true
console.log(true && false); // false
console.log(false && true); // false
console.log(false && false);// false

            

- Logical OR (`||`)

The logical OR operator returns `true` if at least one of the operands is true:

// Logical OR
console.log(true || true);  // true
console.log(true || false); // true
console.log(false || true); // true
console.log(false || false);// false

            

- Logical NOT (`!`)

The logical NOT operator inverts the Boolean value:

// Logical NOT
console.log(!true);  // false
console.log(!false); // true

            

4. Conditional Statements

Booleans are often used in conditional statements like `if`, `else if`, and `else` to control the flow of a program:

- Using `if` Statements

An `if` statement executes code if a condition is true:

// If statement example
let isDay = true;

if (isDay) {
    console.log("It's daytime.");
} else {
    console.log("It's nighttime.");
}

            

- Using `else if` Statements

An `else if` statement allows multiple conditions to be checked:

// Else if statement example
let score = 85;

if (score >= 90) {
    console.log("Grade: A");
} else if (score >= 80) {
    console.log("Grade: B");
} else if (score >= 70) {
    console.log("Grade: C");
} else {
    console.log("Grade: D");
}