trackBy doesn't work as expected

[WuglyakBolgoink]

Hallo!

JavaScript-Demos/demos/ng-for-track-by-pipe2-angular7/app/track-by-property.pipe.ts

Lines 37 to 60 in fa6730f

	if ( Array.isArray( propertyNames ) ) {
	cacheKey = propertyNames.join( "->" );
	// Ensure cached identity function.
	if ( ! cache[ cacheKey ] ) {
	cache[ cacheKey ] = function trackByProperty<T>( index: number, item: T ) : any {
	var values = [];
	// Collect the item values that will be aggregated in the resultant
	// item identity
	for ( var propertyName of propertyNames ) {
	values.push( item[ propertyName ] );
	}
	return( values.join( "->" ) );
	};
	}

This part for a list of properties doesn't work correctly.

the list will be re'rendered each time if I click on refresh button with the same data. If I move the code into separate function and use directly on trackBy, then the list will be never re'rendered...

any Idea?

---

Outputs:

on start:

after click on refresh button: