jsdevtom / distinct-until-changed-immutable

Like distinctUntilChanged(), but with immutable values

Distinct Until Changed Immutable

tl;dr

Install:

npm i -S distinct-until-changed-immutable

then import:

import { distinctUntilChangedImmutable } from 'distinct-until-changed-immutable';

then use:

of({a: 'a'}, {b: 'b'}, {b: 'b'})
  .pipe(
    distinctUntilChangedImmutable(),
  )

---

Returns an Observable that emits all items emitted by the source Observable that are deeply distinct by comparison from the previous item.

If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.

If a comparator function is not provided, a deep equality check is used by default.

Example

A simple example with numbers

import { of } from 'rxjs';
import { distinctUntilChangedImmutable } from 'distinct-until-changed-immutable';

of({a: 'a'}, {b: 'b'}, {b: 'b'}).pipe(
    distinctUntilChangedImmutable(),
  )
  .subscribe(x => console.log(x)); // {a: 'a'}, {b: 'b'}

An example using a compare function

import { of } from 'rxjs';
import { distinctUntilChangedImmutable } from 'distinct-until-changed-immutable';

interface Person {
   age: number,
   name: string
}

of<Person>(
    { age: 4, name: 'Foo'},
    { age: 7, name: 'Bar'},
    { age: 4, name: 'Foo'},
    { age: 6, name: 'Foo'},
  ).pipe(
    distinctUntilChangedImmutable((p: Person /*I have been cloned*/, q: Person) => p === q),
  )
  .subscribe(x => console.log(x));

// displays:
// { age: 4, name: 'Foo' }
// { age: 7, name: 'Bar' }
// { age: 4, name: 'Foo' } // Emitted because the parameters are immutable and we are doing a simple === check in the comparator function above
// { age: 5, name: 'Foo' }

distinct-until-changed-immutable's Issues

Expected identifier error in Internet Explorer 11

The library does not work in Internet Explorer 11.

distinct-until-changed-immutable/src/deep-equals.ts

Line 131 in 08e85f5

for (const [key] of a.entries()) {

ERROR TypeError: Class constructor Subscriber cannot be invoked without 'new'

Getting this error when trying to use the library in an Angular 8 project.

ERROR TypeError: Class constructor Subscriber cannot be invoked without 'new'

This happens only when the target in tsconfig.ts is set to es2015.

A workaround is to set the target to es5 but then this disables differential loading in Angular.