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delta

@rotorsoft/act-root

@rotorsoft/act-root / act-patch/src / delta

Function: delta()

delta<S>(before, after): Readonly<Patch<S>>

Defined in: libs/act-patch/src/delta.ts:26

Compute the smallest Patch<S> that, when applied to before via patch(), yields an object semantically equal to after. The semantic inverse of patch().

Round-trip guarantee: patch(before, delta(before, after)) deeply equals after.

Rules (mirror patch's merging rules):

  • Same reference (Object.is) → omit (mirrors structural sharing)
  • Both plain objects → recurse (mirrors deep merge)
  • Otherwise (any other diff) → set to after[K] (mirrors wholesale replace)
  • Key in before only → set to null (mirrors delete)

Equality is reference-based, matching patch's structural-sharing model. Two structurally-equal-but-distinct values (e.g. two Date instances with the same getTime(), or two arrays with the same elements) are treated as different and emit a replacement — safe for the round-trip identity, just slightly less compact.

Type Parameters​

S​

S extends Schema

Parameters​

before​

Readonly<S>

The original state object

after​

Readonly<S>

The desired state object

Returns​

Readonly<Patch<S>>

The smallest patch that transforms before into after