onFirstData()

onFirstData (alias tapFirst): invoke fn exactly once on the first qualifying value (default where: v => v != null — null/undefined pass through without counting as “first”), then pass all values through unchanged. The one-shot guard is per-node ctx.state (NOT a factory closure, so a second instantiation of the same factory re-arms — R-ctx-state).

Import

import { onFirstData } from "@graphrefly/ts/operators";

Signature

function onFirstData(
  fn: (v: S) => void,
  opts?: { where?: (v: S) => boolean },
): Operator<S, S>

Parameters

Parameter	Type	Description
fn	(v: S) => void	Synchronous function invoked by the helper.
opts	{ where?: (v: S) => boolean }	Options that configure the helper.

Returns

A Operator<S, S> value.

Example

import { onFirstData } from "@graphrefly/ts/operators";

Source

packages/ts/src/graph/operators.ts