Use RxJS operators like debounceTime and distinctUntilChanged to reduce the number of API calls. When building Angular applications that interact with APIs, it is common to have search fields that trigger API calls as the user types. This can lead to a large number of API calls being made, which can slow down the application and put unnecessary strain on the server. By using RxJS operators like debounceTime and distinctUntilChanged, we can reduce the number of API calls and improve the performance of our application.

The debounceTime operator delays the emission of values from an Observable by a specified amount of time. This means that if the user is typing quickly, the API call will only be triggered once they have stopped typing for a certain amount of time. This can significantly reduce the number of API calls being made, as it ensures that only the final search term is used to trigger the API call. For example, if we have a search field that triggers an API call on every key stroke, we can use debounceTime to delay the API call by 500ms, like this:

searchTerm$.pipe(
  debounceTime(500),
  switchMap(searchTerm => this.apiService.search(searchTerm))
).subscribe(results => {
  // handle search results
});

The distinctUntilChanged operator ensures that the API call is only triggered if the search term has changed since the last API call. This means that if the user types the same search term multiple times, the API call will only be triggered once. For example, if we have a search field that triggers an API call on every key stroke, we can use distinctUntilChanged to ensure that the API call is only triggered if the search term has changed, like this:

searchTerm$.pipe(
  debounceTime(500),
  distinctUntilChanged(),
  switchMap(searchTerm => this.apiService.search(searchTerm))
).subscribe(results => {
  // handle search results
});