ComputationNode

A memo or an effect: an owner that reads sources and (for memos) is itself a source.

A memo or an effect: an owner that reads sources and (for memos) is itself a source. Exported from @shadow-js/core/extend as ComputationNode; create one with createComputation and read a memo with readComputation. It owns what its function creates: each run first disposes the children and runs the cleanups of the previous run.

Import#

import { ComputationNode } from "@shadow-js/core/extend";

Signature#

class Computation extends Owner implements Source

Members#

Name	Type	Description
`kind`	`kind: number`	1 for a memo, 2 for an effect.
`state`	`state: number`	How stale the node is: 0 (clean), 1 (a transitive source changed), 2 (a direct source changed).
`flags`	`flags: number`	Engine bit flags (queued, running, disposed, render phase, ...). Read-only outside the engine.
`value`	`value: unknown`	A memo's last value; an effect's last computed value when it has an `apply` stage.
`error`	`error: unknown`	The error a memo's last run threw, rethrown to its readers; undefined when it succeeded.
`equals`	`equals: Equals<unknown>`	A memo's equality: readers are notified only when it says the new value differs.
`fn`	`fn: ((previous: never) => unknown) \| null`	The function each run calls with the previous value; null once disposed.
`apply`	`apply: ((value: never, previous: never) => unknown) \| null`	An effect's second stage, run untracked with the computed value and the previous one; null for none and once disposed.
`sources`	`sources: Edges<Source>`	The sources the last run read, in reading order, as pairs: a source, then the index of this computation in that source's `observers`. Read it with `sourcesOf`, which returns the sources alone.
`observers`	`observers: Edges<Computation> \| null`	The computations that read this memo in their last run, as pairs (see Source.observers).
`stamp`	`stamp`	Stamp of the current run while it tracks, and of the last run that tracked this memo.
`trackIndex`	`trackIndex`	During a run: how many leading entries of `sources` were confirmed again (they keep their edges).
`seq`	`seq: number`	Creation order; breaks ties between effects at equal depth (G-16).
`name`	`name: string \| undefined`	Label shown by devtools and diagnostics.

Examples#

import { createComputation, createSignalNode, readComputation, readSignal } from "@shadow-js/core/extend";

const price = createSignalNode(10, Object.is);
const total = createComputation({ kind: "memo", fn: () => readSignal(price) * 2 });
console.log(readComputation<number>(total)); // 20