v4.0.0 - Use TrackByFunction instead
interface TrackByFn {
}
Nolonger used.
exported from core/index, defined in core/src/change_detection/differs/iterable_differs.ts
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Licensed under the Creative Commons Attribution License 4.0.
https://angular.io/docs/ts/latest/api/core/index/TrackByFn-interface.html