ultirequiem / is-number

🧵 Check if something is a number

is-number

In JavaScript, it's not always as straightforward as it should be to reliably check if a value is a number. It's common for devs to use +, -, or Number() to cast a string value to a number (for example, when values are returned from user input, regex matches, parsers, etc). But there are many non-intuitive edge cases that yield unexpected results:

console.log(+[]); //=> 0
console.log(+""); //=> 0
console.log(+"   "); //=> 0
console.log(typeof NaN); //=> 'number'

Usage

Deno 🦕

import { assertIsNumber, isNumber } from "https://deno.land/x/is_number/mod.ts";

isNumber("hello"); //=> false
isNumber("678"); //=> true
isNumber({}); //=> false
isNumber(+{ a: "34" }); //=> false
isNumber(345); //=> true

assertIsNumber([123]); //=> throws
assertIsNumber({}); //=> throws
assertIsNumber(34); //=> doesn't throws

Node.js 🐢

import { assertIsNumber, isNumber } from "@ultirequiem/is-number";

Browser

You can use any CDN 🔥

Eg. ESM ▶ SkyPack / script tag ▶ JSDelivr.

The API is the same on all this platforms.

Documentation

Autogenerated Documentation

Includes TypeScript type guards, so using it will narrow the type of previously-unknown values.

export function isEven(n: unknown): boolean {
  n++ // Error, n is not a number

  assertIsNumber(n);

  return n % 2 === 0; // OK
}

True Cases

isNumber(5e3);
isNumber(0xff);
isNumber(-1.1);
isNumber(0);
isNumber(1);
isNumber(1.1);
isNumber(10);
isNumber(10.1);
isNumber(100);
isNumber("-1.1");
isNumber("0");
isNumber("012");
isNumber("0xff");
isNumber("1");
isNumber("1.1");
isNumber("10");
isNumber("10.10");
isNumber("100");
isNumber("5e3");
isNumber(parseInt("012"));
isNumber(parseFloat("012"));

False cases

Everything else is false.

isNumber(Infinity);
isNumber(NaN);
isNumber(null);
isNumber(undefined);
isNumber("");
isNumber("   ");
isNumber("foo");
isNumber([1]);
isNumber([]);
isNumber(function () {});
isNumber({});

See the tests for more examples.

CLI Tool

Was done mainly as usage example.

Install

• Node.js 🦍

npm install -g @ultirequiem/is-number

• Deno 🦕

deno install https://deno.land/x/is_number/is-number.ts

Usage

is-number 1 2 hey
true
true
false

Or with the verbose flag 👇

is-number 1 2 hey --verbose
"1" is a number? true
"2" is a number? true
"hey" is a number? false

Support

Open an Issue, I will check it a soon as possible 👀

If you want to hurry me up a bit send me a tweet 😆

Consider supporting me on Patreon if you like my work 🚀

Don't forget to star the repo ⭐

Versioning

We use SemVer for versioning. For the versions available, see the tags.

Authors

Eliaz Bobadilla (a.k.a UltiRequiem) - Creator and Maintainer 💪

See also the full list of contributors who participated in this project.

Licence

Licensed under the MIT License.

is-number's Issues

Add CLI tool

It should work like

is-number hey 123 jk9 # false true  false

Add type assert functions

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions

Delete this.

This should not exist.