Utility Operators

Utility operators in RxJS are a group of operators that are responsible for auxiliary processing of streams (side effects, state control, UI support, etc.) rather than the main purpose of data conversion or filtering.

On this page, operators are categorized by purpose as shown below, and a list is provided to confirm their basic usage. For detailed usage and practical examples, please refer to the respective pages or Practical Use Cases.

List of Operators (by Purpose)

◾ Side Effects and State Control

Operator	Description	Often Combined With
tap	Execute side effects without changing values (log output, UI updates, etc.)	map, switchMap
finalize	Execute cleanup processing when the stream ends	tap, catchError

◾ Timing and Delay Control

Operator	Description	Often Combined With
delay	Delay the emission of each value by a specified time	tap, concatMap
timeout	Generate an error if emission exceeds a certain time	catchError, retry
takeUntil	End subscription when the specified Observable notifies	interval, fromEvent

◾ Initial Value, Repetition, Array Conversion, etc.

Operator	Description	Often Combined With
startWith	Emit an initial value at the beginning of the stream	scan, combineLatest
repeat	Resubscribe to the entire stream after completion	tap, delay
retry	Retry on error	catchError, switchMap
toArray	Emit all values in the stream as a single array (on completion)	concatMap, take

Remarks

• Difference between retry and repeat:
  • retry: Retry on error
  • repeat: Retry on successful completion
• toArray does not output a value unless it completes, so it is commonly used with take() and so on.