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Boolean Data Types in JavaScript

Booleans are a primitive data type in JavaScript. They are used to represent logical values. JavaScript uses the Boolean object to represent true or false.

What is a Boolean in JavaScript?​

In JavaScript, booleans are used to represent logical values. JavaScript uses the Boolean object to represent true or false.

How to Create a Boolean in JavaScript?​

You can create a boolean in JavaScript using the following syntax:

Creating a Boolean in JavaScript
let isTrue = true;
let isFalse = false;

In the above example, isTrue and isFalse are booleans.

Boolean Values​

The boolean data type has only two possible values: true and false. For example:

Boolean Values
let isTrue = true;
let isFalse = false;

Boolean Methods​

The Boolean object has several methods that are used to perform operations on boolean values. For example:

Boolean Methods
let isTrue = true;
let isFalse = false;

console.log(isTrue.toString()); // Output: "true"
console.log(isFalse.valueOf()); // Output: false

In the above example, the toString() method is used to convert a boolean to a string, and the valueOf() method is used to return the primitive value of a boolean.

📝 Note

The Boolean object is a wrapper for a boolean value. It is rarely used in practice, as booleans can be created directly without using the Boolean object.

The Boolean object is not a constructor. It does not have a new operator. It is a function that converts a value to a boolean.

The Boolean object has a single property: prototype. It is the prototype for the Boolean object.

for example:

Boolean Object
let isTrue = true;
let isFalse = false;

console.log(Boolean(isTrue)); // Output: true
console.log(Boolean(isFalse)); // Output: false

In the above example, the Boolean object is used to convert a value to a boolean.

1. What is truthy and falsy in JavaScript?

In JavaScript, a value is considered "falsy" if it converts to false when evaluated in a boolean context. The following values are considered "falsy" in JavaScript:

  • false
  • 0
  • "" (empty string)
  • null
  • undefined
  • NaN (Not a Number)
  • document.all (an object that is present in Internet Explorer)

All other values are considered "truthy" in JavaScript.

For example:

Truthy and Falsy Values
let isTrue = true;
let isFalse = false;

console.log(Boolean(isTrue)); // Output: true
console.log(Boolean(isFalse)); // Output: false
console.log(Boolean(0)); // Output: false
console.log(Boolean("")); // Output: false
console.log(Boolean(null)); // Output: false
console.log(Boolean(undefined)); // Output: false
console.log(Boolean(NaN)); // Output: false
console.log(Boolean(document.all)); // Output: false

In the above example, the Boolean object is used to convert values to booleans. The values 0, "", null, undefined, NaN, and document.all are considered "falsy" in JavaScript.

2. Difference between truthy and falsy

The difference between truthy and falsy is that truthy values are considered true when evaluated in a boolean context, while falsy values are considered false when evaluated in a boolean context.

For example:

Truthy Values

  • true: The boolean value true is considered "truthy" in JavaScript.
  • 1: The number 1 is considered "truthy" in JavaScript.
  • "hello": The string "hello" is considered "truthy" in JavaScript.
  • [] (empty array): An empty array is considered "truthy" in JavaScript.
  • {} (empty object): An empty object is considered "truthy" in JavaScript.
  • function() {} (empty function): An empty function is considered "truthy" in JavaScript.
  • new Date(): A new date is considered "truthy" in JavaScript.
  • Infinity: The value Infinity is considered "truthy" in JavaScript.
  • -Infinity: The value -Infinity is considered "truthy" in JavaScript.
  • 3.14: The number 3.14 is considered "truthy" in JavaScript.

Falsy Values

  • false: The boolean value false is considered "falsy" in JavaScript.
  • 0: The number 0 is considered "falsy" in JavaScript.
  • "" (empty string): An empty string is considered "falsy" in JavaScript.
  • null: The value null is considered "falsy" in JavaScript.
  • undefined: The value undefined is considered "falsy" in JavaScript.
  • NaN: The value NaN is considered "falsy" in JavaScript.
  • 0n: The bigint value 0n is considered "falsy" in JavaScript.
  • -0: The number -0 is considered "falsy" in JavaScript.

for example:

Truthy Values
let isTrue = true;
const num = 1;
const str = "hello";
const arr = [];
const obj = {};
const func = function() {};
const date = new Date();
const inf = Infinity;
const ninf = -Infinity;
const pi = 3.14;

console.log(Boolean(isTrue)); // Output: true
console.log(Boolean(num)); // Output: true
console.log(Boolean(str)); // Output: true
console.log(Boolean(arr)); // Output: true
console.log(Boolean(obj)); // Output: true
console.log(Boolean(func)); // Output: true
console.log(Boolean(date)); // Output: true
console.log(Boolean(inf)); // Output: true
console.log(Boolean(ninf)); // Output: true
console.log(Boolean(pi)); // Output: true
Falsy Values
let isFalse = false;
const zero = 0;
const emptyStr = "";
const nul = null;
const undef = undefined;
const nan = NaN;
const bigZero = 0n;
const negZero = -0;

console.log(Boolean(isFalse)); // Output: false
console.log(Boolean(zero)); // Output: false
console.log(Boolean(emptyStr)); // Output: false
console.log(Boolean(nul)); // Output: false
console.log(Boolean(undef)); // Output: false
console.log(Boolean(nan)); // Output: false
console.log(Boolean(bigZero)); // Output: false
console.log(Boolean(negZero)); // Output: false

Conclusion​

In this tutorial, you learned about the boolean data type in JavaScript, including how to create a boolean, boolean values, and boolean methods. You also learned about the Boolean object and its methods.