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tap ​

Problem ​

You need to insert a side effect (logging, tracking) into a pipeline without breaking the data flow.

Solution ​

Use tap(value, callback) to call callback(value) and return value unchanged.

ts
import { tap } from '@vielzeug/arsenal';

const result = tap(expensiveComputation(), (v) => console.log('computed:', v));
// result is the computed value; the log is a side effect

In a pipe ​

ts
import { pipe, tap } from '@vielzeug/arsenal';

const process = pipe(
  (s: string) => s.trim(),
  (s) => tap(s, (v) => console.log('after trim:', v)),
  (s) => s.toUpperCase(),
);

Pitfalls ​

  • The callback's return value is ignored. tap always returns the original value.