# MobX 6.16.0

- Product: MobX (https://whatsnew.fyi/product/mobx)
- Vendor: MobX
- Date: 2026-06-03
- Version: 6.16.0
- Original notes: https://github.com/mobxjs/mobx/releases/tag/mobx%406.16.0
- Permalink: https://whatsnew.fyi/product/mobx/releases/6.16.0

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **changed** — Make the 2022.3 @computed decorator lazy by creating ComputedValue on first read of the decorated getter rather than eagerly during instance construction
- **changed** — Make the 2022.3 @observable accessor decorator lazy by creating ObservableValue on first read/write/observe of the decorated accessor rather than eagerly during instance construction
- **fixed** — Fix regression where isComputedProp returned false for lazy @computed properties before first read
- **added** — Add getOrInsert and getOrInsertComputed to ObservableMap for compatibility with ESNext Map typings

###### Minor Changes

-   [`6b3fb0ee725c0521bbaf7ba901a30261472a0e71`](https://github.com/mobxjs/mobx/commit/6b3fb0ee725c0521bbaf7ba901a30261472a0e71) [#4639](https://github.com/mobxjs/mobx/pull/4639) Thanks [@ashishkr96](https://github.com/ashishkr96)! - feat(mobx): make the 2022.3 `@computed` decorator lazy. `ComputedValue` is now created on first read of the decorated getter rather than eagerly during instance construction, avoiding wasted allocations for getters that are never used. On a 50k-instance × 10-getter class with one read per instance this cuts construction heap by ~50% and construction time by ~25%; the steady-state read path is unchanged. Closes #4616.

-   [`f0c68749428fd4d3bba48e9685e44fd1ddbbee76`](https://github.com/mobxjs/mobx/commit/f0c68749428fd4d3bba48e9685e44fd1ddbbee76) [#4658](https://github.com/mobxjs/mobx/pull/4658) Thanks [@ashishkr96](https://github.com/ashishkr96)! - feat(mobx): make the 2022.3 `@observable accessor` decorator lazy. `ObservableValue` is now created on first read/write/observe of the decorated accessor rather than eagerly during instance construction, avoiding wasted allocations for fields that are never touched. On a 50k-instance × 10-field class with sparse access (1 of 10 fields read per instance), this cuts construction heap by ~82% and construction time by ~86% versus the eager path. Follow-up to #4639.

###### Patch Changes

-   [`7eb54418b16fb9b415c04c5b8e05779790dd74ed`](https://github.com/mobxjs/mobx/commit/7eb54418b16fb9b415c04c5b8e05779790dd74ed) [#4659](https://github.com/mobxjs/mobx/pull/4659) Thanks [@kubk](https://github.com/kubk)! - Fix regression from #4639 where isComputedProp returned false for lazy @computed properties before first read

-   [`c22b4b705447a4ccdce93473255f4beb170613f3`](https://github.com/mobxjs/mobx/commit/c22b4b705447a4ccdce93473255f4beb170613f3) [#4657](https://github.com/mobxjs/mobx/pull/4657) Thanks [@kubk](https://github.com/kubk)! - Add `getOrInsert` and `getOrInsertComputed` to `ObservableMap` for compatibility with ESNext `Map` typings.