is-has

Set of checking functions. No deps! Never throws errors!

Installation

npm i is-has

Functions

hasOwnProperty

declare function hasOwnProperty<T = object>(obj: T, key: keyof T): key is keyof T;
declare function hasOwnProperty(obj: any, key: any): key is keyof obj;

hasOwnProperty checks if obj has its own property. The result is fully compatible with Object.hasOwn.

import {hasOwnProperty} from 'is-has';

class Class1 {
  propA: string = 'propA';
  static propB: string = 'static propB';
  #propC: string = '#propC';
  static #propD: string = 'static #propD';

  get propC() {
    return this.#propC;
  }

  static get propD() {
    return this.#propD;
  }

  functionA() {
    return 'functionA';
  }

  static functionB() {
    return 'functionB';
  }
}

const classInstance = new Class1();

const obj = {
  propA: 'propA',
  get propB() {
    return 'propB';
  },
};

const arr = [1, '2', 3, 'aaa'];

hasOwnProperty(Class1, 'propA');     // false
hasOwnProperty(Class1, 'propB');     // true
hasOwnProperty(Class1, 'propC');     // false
hasOwnProperty(Class1, 'propD');     // true
hasOwnProperty(Class1, 'functionA'); // false
hasOwnProperty(Class1, 'functionB'); // true

hasOwnProperty(classInstance, 'propA');     // true
hasOwnProperty(classInstance, 'propB');     // false
hasOwnProperty(classInstance, 'propC');     // false
hasOwnProperty(classInstance, 'propD');     // false
hasOwnProperty(classInstance, 'functionA'); // false
hasOwnProperty(classInstance, 'functionB'); // false

hasOwnProperty(obj, 'propA'); // true
hasOwnProperty(obj, 'propB'); // true
hasOwnProperty(obj, 'propC'); // false
hasOwnProperty(obj, null);    // false

hasOwnProperty(arr, 0);         // true
hasOwnProperty(arr, 4);         // false
hasOwnProperty(arr, 'length');  // true
hasOwnProperty(arr, 'aaa');     // false
hasOwnProperty(arr, null);      // false
hasOwnProperty(arr, undefined); // false

hasOwnProperty('obj', 'propA');       // false
hasOwnProperty(123, 'propC');         // false
hasOwnProperty(null, null);           // false
hasOwnProperty(undefined, undefined); // false

isNumber

declare function isNumber(variable?: unknown): variable is number;

isNumber checks if a variable is a number.

• Both Infinity and NaN are treated as non-numbers.
• BigInt is a separate story in JS, so it's not treated as a number as well.

import {isNumber} from 'is-has';

isNumber(0);     // true
isNumber('0');   // false
isNumber('hi');  // false
isNumber(0 / 0); // false
isNumber(1 / 0); // false
isNumber(123n);  // false

isString

declare function isString(variable?: unknown): variable is string;

isString checks if variable is a string.

import {isString} from 'is-has';

isString(123);      // false
isString('Hello!'); // true