githubmirror/immutable-js

website/docs/ValueObject.mdx

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Julien Deniau

Doc as mdx instead of export from .d.ts file (#2104)

24 май 2025, 00:47

24 май 2025, 00:4721de701

import Repl from '@/repl/Repl.tsx';
import CodeLink from '@/mdx-components/CodeLink.tsx';

# ValueObject

The interface to fulfill to qualify as a Value Object.

## Members

<MemberLabel label="equals" />

True if this and the other Collection have value equality, as defined
by `Immutable.is()`.

<Signature code="equals(other: unknown): boolean;" />

Note: This is equivalent to `Immutable.is(this, other)`, but provided to
allow for chained expressions.

<MemberLabel label="hashCode" />
Computes and returns the hashed identity for this Collection.

<Signature code={`hashCode(): number;`} />

The `hashCode` of a Collection is used to determine potential equality,
and is used when adding this to a `Set` or as a key in a `Map`, enabling
lookup via a different instance.

<Repl
  defaultValue={`const a = List([1, 2, 3]);
const b = List([1, 2, 3]);
// a and b are different instances
const set = Set([a]);
set.has(b)`}
/>

Note: hashCode() MUST return a Uint32 number. The easiest way to
guarantee this is to return `myHash | 0` from a custom implementation.

If two values have the same `hashCode`, they are [not guaranteed
to be equal][Hash Collision]. If two values have different `hashCode`s,
they must not be equal.

Note: `hashCode()` is not guaranteed to always be called before
`equals()`. Most but not all Immutable.js collections use hash codes to
organize their internal data structures, while all Immutable.js
collections use equality during lookups.

[Hash Collision]: https://en.wikipedia.org/wiki/Collision_(computer_science)