whenNilPipe for angular

whennil.pipe.spec.ts

/*
 * @author RKlein
 */

import { WhenNilPipe } from "./whennil.pipe";

    describe('WhenNilPipe', () => {

        it('converts null to "--"', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform(null, "--")).toEqual("--");
        });

        it('converts undefined to "--"', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform(undefined, "--")).toEqual("--");
        });

        it('leaves a defined string alone', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform("We are not nil", "--")).toEqual("We are not nil");
        });

        it('leaves a defined number alone', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform(42, "--")).toEqual(42);
        });

        it('does *not* convert an empty string to "--"', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform('', "--")).toEqual('');
        });

        it('*does* convert an empty string to "--" if we explicitly say so', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform('', "--", true)).toEqual('--');
        });

        it('does *not* convert an empty array to "--"', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform([], "--")).toEqual([]);
        });

        it('*does* convert an empty array to "--" if we explicitly say so', () => {
            let converter = new WhenNilPipe();
            expect(converter.transform([], "--", true)).toEqual('--');
        });

    });

whennil.pipe.ts

/*
 * @author RKlein
 */

import { Injectable, Pipe, PipeTransform } from '@angular/core';
import * as _ from 'lodash';

/**
 * If the value is null/undefined just display an alternative text
 * Usage Demo:
 ```html
 <div>{{result?.value|whenNil:'--'}}</div>
 ```
 * If any empty string or empty collection should also trigger the empty text then add true as last parameter
 */
@Pipe({
    name: 'whenNil'
})
@Injectable()
export class WhenNilPipe implements PipeTransform {
    transform(value: any, nilText: string, emptyAlso:boolean=false): string {
        if (_.isNil(value)) {
            return nilText;
        }
        if(emptyAlso && _.isEmpty(value)){
            return nilText;
        }
        return value;
    }
}