@technically/is-not-undefined

@technically/is-not-undefined is a micro-package to check if a value is not null. With proper TS typing!

Usage

import { isNotUndefined } from '@technically/is-not-undefined';

const values = ['hello', 'world', undefined];

const uppercase = values.filter(isNotUndefined).map((value) => {
  return value.toUpperCase(); // OK
});

Why

In Typescript, it is often needed to filter out undefined from a list of values, and then process them.

The problem is that Boolean does not currently work as a type-guard in Typescript:

const values = ['hello', 'world', undefined];

const uppercase = values.filter(Boolean).map((value) => {
  return value.toUpperCase(); // TS18048: 'value' is possibly 'undefined'.
});

To mitigate the issue you have to wrap Boolean into a type-guard function like this:

const values = ['hello', 'world', undefined];

const uppercase = values.filter((x): x is Exclude<typeof x, undefined> => Boolean(x)).map((value) => {
  return value.toUpperCase(); // OK
});

To avoid writing these ad-hoc type-guards every time, I've created this package.

Related packages

• @technically/is-not-null

License

MIT

Credits

Authored by Ivan Voskoboinyk.