isNumber

Checks if a value is a number (excluding NaN).

Implementation

View Source Code

/**
 * Determines if the passed value is a number.
 *
 * @example
 * ```ts
 * isNumber(123); // true
 * isNumber('hello world'); // false
 * ```
 *
 * @param arg - The argument to be checked.
 *
 * @returns `true` if the value is a number, else `false`.
 */
export function isNumber(arg: unknown): arg is number {
  return typeof arg === 'number' && !Number.isNaN(arg);
}

export const IS_NUMBER_ERROR_MSG = 'Expected a number';

Features

• Type Guard: Narrows unknown to number
• NaN Exclusion: Returns false for NaN values
• Isomorphic: Works in both Browser and Node.js

API

function isNumber(value: unknown): value is number;

Parameters

• value: The value to check

Returns

• true if the value is a number (and not NaN), false otherwise

Examples

Basic Usage

import { isNumber } from '@vielzeug/toolkit';

isNumber(42); // true
isNumber(3.14); // true
isNumber(NaN); // false
isNumber('42'); // false
isNumber(Infinity); // true

Type Guard Usage

import { isNumber } from '@vielzeug/toolkit';

function calculate(value: unknown) {
  if (isNumber(value)) {
    // TypeScript knows value is number here
    return value * 2;
  }
  return 0;
}

Implementation Notes

• Explicitly excludes NaN (since typeof NaN === 'number' in JavaScript)
• Returns true for Infinity and -Infinity
• Use for validation and type narrowing in TypeScript

See Also

• isString: Check if value is a string
• isPrimitive: Check if value is a primitive type
• isPositive: Check if number is positive
• isNegative: Check if number is negative
• typeOf: Get the type of any value