TypeScript Booleans

Note: If you're new to TypeScript, check our Getting Started with TypeScript tutorial first.

In TypeScript, booleans are primitive data types that can either be true or false. For example,

let a = true;
let b = false;

let a = 'true';
console.log(typeof a); // string

Booleans Results of Operators

The comparison and logical operators in TypeScript always return boolean values.

1. TypeScript Boolean With Comparison Operators

let age: number = 18;

// Check if age is greater than or equal to 18
let isAdult: boolean = age >= 18;

console.log(isAdult); // true

Here, age >= 18 evaluates if age is greater than or equal to 18 and assigns the result (true or false) to isAdult.

2. TypeScript Boolean With Logical Operators

let age: number = 18;
// Assign boolean value 'true' to hasConsent
let hasConsent: boolean = true;

let canDrive = age >= 16 && hasConsent; 
console.log(canDrive);  // true

In the above program, age >= 16 && hasConsent checks if age is greater than or equal to 16 and if hasConsent is true.

Here, the value of age >= 16 is true. Since both age >= 16 and hasConsent are true, the value of canDrive is also true.

let hasPermission: boolean = true;

// Boolean with if...else
if (hasPermission) {
    console.log("Access granted");
}
else {
    console.log("Access denied");
}

Access granted

// Boolean with for loop
for (let i: number = 0; i < 3; i++) {
    console.log("Loop iteration:", i);
}

Loop iteration: 0
Loop iteration: 1
Loop iteration: 2

TypeScript Boolean() Function

The Boolean() function is used to convert various data types to boolean values. For example,

let a: string = "true";
console.log(Boolean(a)); // true

Everything with a value returns true. For example,

let result: boolean;

// Convert a positive number to boolean
result = Boolean(20);
console.log(result); // true
console.log(typeof result); // boolean

// Convert a negative number to boolean
result = Boolean(-20);
console.log(result); // true

// Convert a string to boolean
result = Boolean("hello");
console.log(result); // true

// Create an object
let obj = {a: 1};

// Convert the object to boolean
result = Boolean(obj)
console.log(result); // true

In TypeScript, undefined, null, 0, NaN, '' converts to false. For example,

let result: boolean;

// Convert empty string to boolean
result = Boolean('');
console.log(result); // false

// Convert 0 to boolean
result = Boolean(0);
console.log(result); // false

// Convert undefined to boolean
result = Boolean(undefined);
console.log(result); // false

// Convert null to boolean
result = Boolean(null);
console.log(result); // false

// Convert NaN to boolean
result = Boolean(NaN);
console.log(result); // false

Note: If you want to learn more about the boolean conversion, visit TypeScript Type Conversion.

Boolean Objects

You can create a boolean object using the new keyword. For example,

let a: boolean = true;

// Create a boolean object
let b = new Boolean(true);

console.log(a); // true
console.log(b); // [Boolean: true]

console.log(typeof a); // "boolean"
console.log(typeof b); // "object"

Output

true
[Boolean: true]
boolean
object

Note: It is recommended to avoid using boolean objects since it slows down the program.

TypeScript Boolean Methods

Some built-in boolean methods in TypeScript are:

Example: Convert Boolean to String

let count: boolean = false;

// Convert the count variable to string
let result: string = count.toString();

console.log(result);
console.log(typeof result);

Output

false
string

Here, we have converted the boolean variable count to string using the toString() method.

Example: Boolean valueOf() Method

// Create a boolean object
let boolObj = new Boolean(true);

// Get the primitive value of boolObj
let result: boolean = boolObj.valueOf();

console.log(boolObj); //  [Boolean: true]
console.log(result); // true

console.log(typeof boolObj); // "object"
console.log(typeof result); // "boolean"

Output

[Boolean: true]
true
object
boolean

Here, boolObj.valueOf() returns the primitive value of the boolean object boolObj.

Note: A primitive value of a boolean object is just the raw boolean value stored in the object, i.e., true or false.

Also Read:

• TypeScript typeof Operator
• TypeScript for Loop
• TypeScript if…else Statement