Breaking Changes

• Eliminate NonEmptyObject by @thegedge in https://github.com/mobxjs/mobx-state-tree/pull/2152
• Improved typing for union types by @thegedge in https://github.com/mobxjs/mobx-state-tree/pull/2151
• fix #1530 array clear replace should produce one patch by @BrianHung in https://github.com/mobxjs/mobx-state-tree/pull/2073
• Feat/has env and getenv changes by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2163

Features

• Added a new feature, hasEnv, to support https://github.com/mobxjs/mobx-state-tree/pull/2163

Fixes

• Union types will now be fixed, but this also may break TypeScript for some users
• Array operations produce condensed patches when we can, but this may break for some users who relied on the patch generation as it was
• fix: do not mutate properties object by model constructor by @dangreen in https://github.com/mobxjs/mobx-state-tree/pull/2176
• Fix/get members 2173 by @evinosheaforward in https://github.com/mobxjs/mobx-state-tree/pull/2174
• fix: #2138 linter issues with fail function by @JuanJo4 in https://github.com/mobxjs/mobx-state-tree/pull/2171

Tests

• Test: convert to bun:test for our tests, remove codecov by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2149

Docs

• Docs/update docs homepage by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2141
• docs: fix typos in docs update by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2142
• Docs: add comparison between React Context/Reducer by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2158 Docs: add recipe for mst-form-type by @sherlockwang in https://github.com/mobxjs/mobx-state-tree/pull/2168
• docs: fix broken link by @kylemeenehan in https://github.com/mobxjs/mobx-state-tree/pull/2165
• docs: update TypeScript tips by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2166
• docs: add recipe for auto-generated property setters by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2169
• docs: correct bun run test to bun run test:all for new contributers by @evinosheaforward in https://github.com/mobxjs/mobx-state-tree/pull/2177

Community/Developer Changes

• Chore/use bun as a package manager and script runner by @coolsoftwaretyler in https://github.com/mobxjs/mobx-state-tree/pull/2148
• Bump typescript from 3.9.10 to 5.3.3 by @thegedge in https://github.com/mobxjs/mobx-state-tree/pull/2146
• chore: remove unused, unnecessary custom Omit type #2167

New Contributors

• @thegedge made their first contribution in https://github.com/mobxjs/mobx-state-tree/pull/2146
• @sherlockwang made their first contribution in https://github.com/mobxjs/mobx-state-tree/pull/2168
• @dangreen made their first contribution in https://github.com/mobxjs/mobx-state-tree/pull/2176
• @evinosheaforward made their first contribution in https://github.com/mobxjs/mobx-state-tree/pull/2174

Full Changelog: https://github.com/mobxjs/mobx-state-tree/compare/v5.4.2...v6.0.0

Migration Guide from v5 to v6

TypeScript update

Make sure you're using TypeScript 5.3.3, and you have the following compiler flags:

{
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "noImplicitAny": true,
    "noImplicitReturns": true,
    "noImplicitThis": true
}

Or the shorthand:

{
  "strict": true,
  "noImplicitReturns": true
}

Removing $nonEmptyObject

We removed the $nonEmptyObject key from the ModelCreationType. For the most part, this was an internal feature that would only have shown up in TypeScript errors. There is no runtime change, but if you have any custom typings that relied on something like [$nonEmptyObject] - you should be able to eliminate those.

Union Type Changes

In the past, named enumerations had more specific type than unnamed enumerations. You may have some TypeScript errors where you were using anonymous enumerations. You can type those with the union of literal values inside the enumeration now.

import { t } from "mobx-state-tree";

/**
 * In MobX-State-Tree 5.4.1, this is typed as:
 * ISimpleType<"Red" | "Orange" | "Green">
 */
const namedEnum = t.enumeration("Color", ["Red", "Orange", "Green"]);

/**
 * In MobX-State-Tree 5.4.1, this is typed as:
 * ISimpleType<string>
 */
const anonymousEnum = t.enumeration(["Red", "Orange", "Green"]);

/**
 * If you use mobx-state-tree@^6.0.0, both of these will be typed as:
 * ISimpleType<"Red" | "Orange" | "Green">
 */

This has also fixed https://github.com/mobxjs/mobx-state-tree/issues/1525 and https://github.com/mobxjs/mobx-state-tree/issues/1664

For #1525, If you had models with properties that were unions including other models, you may have done some type assertions to resolve the issue. This should no longer be necessary. In most cases, we don't expect this to show up as errors. But the inferred types have changed. Look through your codebase for unions of models in the properties of other models, and if you hit any issues, you may be able to use better typing form here on out.

The issue presented itself in #1664 when using types with different creation and instance types which were passed to unions inside of arrays. If you see more TypeScript errors aside from the other items mentioned, look for types.union that creates a union which includes Array, Map, or Model types. If you had any custom type assertions, you may no longer need those.

Array operation patch changes

When an Array type calls clear, or splices itself from index 0, the generated patch is different. We have shortened the operations to be a patch like:

op: "replace", path: "", value: []

If you use onPatch and expect any specific shape of patches from Array.clear or Array.splice, you may need to update your app logic to handle the changed patch generation.

getEnv now throws

If you call getEnv and there is no environment, it will now throw an error. Previously, it would return an empty object.

Check your codebase for getEnv calls, and guard against this error with hasEnv, which will return true if the current state tree has an environment, or false if not.