typed-empty-fields-filter

What is it?

A simple package for filtering arrays of objects, leaving out items based on null or undefined in given fields, while at the same time providing propert typing for the resulted items.

The package includes 3 functions

• filterNullFields for filtering fields with null values;
• filterUndefinedFields for filtering fields with undefined values;
• filterEmptyFields for filtering both null and undefined values at the same time.

For example

Provided you have an interface with a field or fields which can be undefined

interface Point {
    x?: number;
    y?: number;
}

Given an array of such items, you can filter them out and have the proper typing for a returned items in the new array:

const points: Array<Point> = [{x: 2}, { y: 2 }, {x: 1, y: 1}];

// result array type will be Array<{x?: number; y: number}>
const filteredWithYRequired = filterEmptyFields(points, 'y');

// resulting interface has y as 'number', not 'number | undefined' union as before
filteredWithYRequired[0]?.y;

or filter based on a set of fields:

const points: Array<Point> = [{x: 2}, { y: 2 }, {x: 1, y: 1}];

// result array type will be Array<{x: number; y: number}>
const filteredWithYRequired = filterEmptyFields(points, ['x', 'y']);

Installation

npm i --save @merry-solutions/typed-empty-fields-filter

Import

import {filterEmptyFields, filterNullFields, filterUndefinedFields} from '@merry-solutions/typed-empty-fields-filter';

Usage

Pick one of the three function and pass an array and a filed/list of fields for filtering. Intellisense will help you out.

import {filterEmptyFields, filterNullFields, filterUndefinedFields} from '@merry-solutions/typed-empty-fields-filter';

export interface User {
  id: number;
  surname: string;
  name?: string;
  middleName: string | undefined;
  phone?: string | null;
  hobby?: string | null;
}

const USERS: Array<User> = [
  {
    id: 1,
    surname: 'Tann',
    middleName: 'XtraCare Wet Wipes',
    phone: '750-476-2058',
    hobby: 'transform one-to-one vortals',
  },
  {
    id: 2,
    name: 'Emylee',
    surname: 'Langelaan',
    middleName: undefined,
    phone: null,
  },
  {
    id: 3,
    name: 'Silvanus',
    surname: 'Bewsy',
    middleName: 'daytime cold and flu',
    phone: '999-831-0154',
    hobby: null,
  },
  {
    id: 4,
    name: 'Leroi',
    surname: 'Dragge',
    middleName: 'Monistat 7 Combination Pack',
    phone: null,
    hobby: 'evolve interactive vortals',
  },
];

// only users with non-null and non-undefined hobbies, hobby is 'string'
const u1 = filterEmptyFields(USERS, 'hobby');

// only users with non-null and non-undefined name, middleName, phone, hobby
const u2 = filterEmptyFields(USERS, ['name', 'middleName', 'phone', 'hobby']);


// only users with non-null phone, phone is 'undefined | string'
const u3 = filterNullFields(USERS, 'phone');

// same as above, array example
const u4 = filterNullFields(USERS, ['phone']);

// only users with non-undefined phone, phone is 'null | string'
const u5 = filterUndefinedFields(USERS, 'phone');

// same as above, array example
const u6 = filterUndefinedFields(USERS, ['phone']);

That's all.