Remove undefined keys¶

removeUndefinedKeys is a built‑in normalization rule that removes object keys whose values are undefined.

This produces a cleaner and more predictable object shape by stripping absent or uninitialized fields. If the value is not a plain object, or no keys contain undefined, no normalization step is emitted.

Signature¶

export const removeUndefinedKeys: NormalizationRule<unknown>
(value: unknown, mode: NormalizationMode, path: FieldPath) => NormalizationStep[]

Events¶

Event code	Description
`object.without.undefined-keys`	Keys with `undefined` values were removed.

Design rationale¶

Removes only keys whose values are exactly undefined.
Preserves all defined values, including null, empty strings, empty arrays, and empty objects (handled by other rules).
Eliminates uninitialized or absent fields commonly produced by partial form submissions, spread operations, or API hydration.
Emits a normalization step only when at least one undefined key is removed.
Classified as lossy normalization — the original undefined values are discarded.
Produces a stable, predictable object shape for downstream validators, scanners, and policy layers.

Invoke¶

removeUndefinedKeys runs automatically when:

The value is structurally a plain object (not an array).
The normalization stage is active.
The current mode allows lossy normalization.

Mode behavior:

strict: Rule does not run (lossy).
moderate: Rule does not run (lossy).
lax: Rule runs.

Normalization cannot be invoked manually. It is always applied automatically based on structural type and mode.

Examples¶

Undefined keys removed¶

const value = {
  name: "Alice",
  age: undefined,
  meta: undefined
};

const result = removeUndefinedKeys(value, "lax", "$");
// → [
//     {
//       path: "$",
//       nextValue: { name: "Alice" },
//       lossy: "lossy",
//       events: [
//         JaneEvent{ kind: "info", code: "object.without.undefined-keys", ... }
//       ]
//     }
//   ]

No undefined values — no normalization¶

const result = removeUndefinedKeys({ a: 1, b: undefined }, "strict", "$");
// → []

Non‑object value¶

const result = removeUndefinedKeys("not an object", "lax", "$");
// → []