To sum up, the big change in 5.0 is a Typescript change related to Map that is typed closer to the JS object. This is a huge change for TS users, but do not impact the runtime behavior. (see Improve TypeScript definition for Map for more details)

Other breaking changes are:

[BREAKING] Remove deprecated methods:

Released in 5.0.0-rc.1

Map.of('k', 'v'): use Map([ [ 'k', 'v' ] ]) or Map({ k: 'v' })
Collection.isIterable: use isIterable directly
Collection.isKeyed: use isKeyed directly
Collection.isIndexed: use isIndexed directly
Collection.isAssociative: use isAssociative directly
Collection.isOrdered: use isOrdered directly

[BREAKING] `OrdererMap` and `OrderedSet` hashCode implementation has been fixed

Released in 5.0.0-rc.1

Fix issue implementation of hashCode for OrdererMap and OrderedSet where equal objects might not return the same hashCode.

Changed in #2005

[BREAKING] Range function needs at least two defined parameters

Released in 5.0.0-beta.5

Range with undefined would end in an infinite loop. Now, you need to define at least the start and end values.

If you need an infinite range, you can use Range(0, Infinity).

Changed in #1967 by @jdeniau

[Minor BC break] Remove default export

Released in 5.0.0-beta.1

Immutable does not export a default object containing all it's API anymore. As a drawback, you can not immport Immutable directly:

- import Immutable from 'immutable';
+ import { List, Map } from 'immutable';

- const l = Immutable.List([Immutable.Map({ a: 'A' })]);
+ const l = List([Map({ a: 'A' })]);

If you want the non-recommanded, but shorter migration path, you can do this:

- import Immutable from 'immutable';
+ import * as Immutable from 'immutable';

  const l = Immutable.List([Immutable.Map({ a: 'A' })]);

[TypeScript Break] Improve TypeScript definition for `Map`

Released in 5.0.0-beta.1

If you do use TypeScript, then this change does not impact you : no runtime change here. But if you use Map with TypeScript, this is a HUGE change ! Imagine the following code

const m = Map({ length: 3, 1: 'one' });

This was previously typed as Map<string, string | number>

and return type of m.get('length') or m.get('inexistant') was typed as string | number | undefined.

This made Map really unusable with TypeScript.

Now the Map is typed like this:

MapOf<{
    length: number;
    1: string;
}>

and the return type of m.get('length') is typed as number.

The return of m.get('inexistant') throw the TypeScript error:

Argument of type '"inexistant"' is not assignable to parameter of type '1 | "length"

If you want to keep the old definition

This is a minor BC for TS users, so if you want to keep the old definition, you can declare you Map like this:

const m = Map<string, string | number>({ length: 3, 1: 'one' });

If you need to type the Map with a larger definition

You might want to declare a wider definition, you can type your Map like this:

type MyMapType = {
  length: number;
  1: string | null;
  optionalProperty?: string;
};
const m = Map<MyMapType>({ length: 3, 1: 'one' });

Keep in mind that the MapOf will try to be consistant with the simple TypeScript object, so you can not do this:

Map({ a: 'a' }).set('b', 'b');
Map({ a: 'a' }).delete('a');

Like a simple object, it will only work if the type is forced:

Map<{ a: string; b?: string }>({ a: 'a' }).set('b', 'b'); // b is forced in type and optional
Map<{ a?: string }>({ a: 'a' }).delete('a'); // you can only delete an optional key

Are all `Map` methods implemented ?

For now, only get, getIn, set, update, delete, remove, toJS, toJSON methods are implemented. All other methods will fallback to the basic Map definition. Other method definition will be added later, but as some might be really complex, we prefer the progressive enhancement on the most used functions.

Fixes

Fix type inference for first() and last() #2001 by @butchler
Fix issue with empty list that is a singleton #2004 by @jdeniau
Map and Set sort and sortBy return type #2013 by @jdeniau

Internal

[Internal] Migrating TS type tests from dtslint to TSTyche #1988 and #1991 by @mrazauskas. Special thanks to @arnfaldur that migrated every type tests to tsd just before that.
[internal] Upgrade to rollup 3.x #1965 by @jdeniau
[internal] upgrade tooling (TS, eslint) and documentation packages: #1971, #1972, #1973, #1974, #1975, #1976, #1977, #1978, #1979, #1980, #1981