Checks if any value is a boolean type, or the obtained type from its object class equal to 'boolean', or an object type and an instance of Boolean that is equal to true or false.

const isBoolean = <
  Type extends AnyBoolean = boolean,
  Payload extends object = object
  value: any,
  callback: ResultCallback<any, Payload> = resultCallback,
  payload?: Payload
): value is Type =>
    (typeof value === 'boolean' ||
    typeOf(value) === 'boolean' ||
    (typeof value === 'object' && value instanceof Boolean)) &&
    (value.valueOf() === true || value.valueOf() === false),

Generic type variables


The Type generic type variable constrained by generic type AnyBoolean by default of boolean indicates the type of the given value via the return type.


The Payload generic type variable constrained by object indicates the type of optional parameter payload of the supplied callback function and payload optional parameter of the isBoolean() function from which it captures its value.


value: any

The value of any type to check.

callback: ResultCallback<any, Payload>

A callback function of ResultCallback type with parameters, the value that has been checked, the result of this check, and payload of generic type variable Payload with optional properties from the provided payload, to handle them before the result return. By default, it uses resultCallback() function.

payload?: Payload

An optional object of the generic type variable Payload is assigned to the payload of the given callback function.

Return type

value is Type

The return type is a boolean as the result of its statement, indicating the value is a generic type variable Type constrained by AnyBoolean by default equal to the boolean.


The return value is a boolean indicating whether the provided value is a boolean type or an instance of Boolean.

Example usage

Basic example

// Basic example usage.
import { isBoolean } from '@angular-package/type';

isBoolean(false); // Returns `true` as `value is boolean`
isBoolean(new Boolean(false)); // Returns `true` as `value is boolean`

Parameters callback and payload

// Callback and payload parameters example usage.
import { isBoolean } from '@angular-package/type';

isBoolean('my name', (result, value, payload) => {
  if (result === false) {
    value // "my name"
    if (payload) {
      // Change the result from `false` to `true`.
      if (payload === payload.accepted) {
        result = true;
  return result;
}, { accepted: 'my name' }); // Returns `true` as `value is boolean`.

String as boolean

// String as boolean example usage.
import { isBoolean } from '@angular-package/type';

const fakeBoolean = new String('');

Object.assign(fakeBoolean, {
  get [Symbol.toStringTag](): string {
    return 'boolean';

isBoolean(fakeBoolean); // false
typeOf(fakeBoolean); // "boolean"
typeof fakeBoolean; // "object"

Boolean as string

// Boolean as string example.
import { isBoolean } from '@angular-package/type';

const stringAsBoolean = new Boolean('');

Object.assign(stringAsBoolean, {
  get [Symbol.toStringTag](): string {
    return 'string';

isBoolean(stringAsBoolean); // true
typeOf(stringAsBoolean); // "string"
typeof stringAsBoolean; // "object"

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