`spy`

Executes a side-effect function for each signal without modifying the stream. Also exported as tap for RxJS compatibility.

Signature

function spy<T extends Signal>(fn: (signal: T) => void): Operator<T, T>

Aliases

spy - Primary name
tap - RxJS-compatible alias

Example

import { singlePointer } from "cereb";
import { spy } from "cereb/operators";

singlePointer(element)
  .pipe(
    spy((signal) => {
      console.log(signal.value.x, signal.value.y);
    })
  )
  .on(handlePointer);

Use Cases

Debug Logging

pan(element)
  .pipe(spy((s) => console.log("Pan:", s.value.phase, s.value.deltaX)))
  .on(handlePan);

Prevent Default

wheel(element, { passive: false })
  .pipe(
    when(zoomMode$),
    spy((s) => s.value.originalEvent.preventDefault())
  )
  .on(handleZoomWheel);

Analytics / Metrics

pan(element)
  .pipe(
    spy((s) => {
      if (s.value.phase === "end") {
        analytics.track("pan_complete", { distance: s.value.distance });
      }
    })
  )
  .on(handlePan);