All five utilities mutate target in place and return it for convenience; the returned reference is the same object you passed in.

Wraps value in a proxy that turns every property into a signal, recursively. Both existing and new properties are tracked and mutable. Reads of keys that don't exist yet are still tracked — once the key is added, readers re-run.

mutable(obj) modifies obj in place so the original reference stays reactive (and identity methods like === keep working). Pass true as the second argument to copy the input first, leaving the original untouched.

Like mutable, but shallow: only the target's own properties become tracked getters/setters. Nested objects stay plain objects. Useful for opt-in reactivity on a handful of keys without walking the whole tree.

Pass a keys array to signalify only the properties you name. The keys don't have to exist yet — reads of a missing key are tracked and will re-run once the key is assigned.

Reconciling data can be confusing — there are three APIs so each use case stays narrow and explicit. In every case, the references to unchanged properties are kept intact.

All three accept an optional keys option (third argument on merge / replace) that tells the reconciler how to identify items inside nested arrays. Without it, entries are matched by index; with it, they are matched by the named key and references to unchanged items are preserved across reorderings.

Merges source into target. Keys of target that are absent from source are left alone.

Merges source into target and deletes any keys of target that aren't in source.

Overwrites keys of target that appear in source. Unlike replace, keys of target not in source are kept.