# Size change log

A running record of how each correctness/feature change affects the `WebComponent` base class bundle, measured as min + brotli via [size-limit](https://github.com/ai/size-limit). Baseline before the Phase 0 correctness work: **1.19 kB** (limit 1.2 kB).

| Change                                                           | Size (min+brotli)  | Limit         | Reason & benefit                                                                                                                                                                                                                                                                                                                                                 |
| ---------------------------------------------------------------- | ------------------ | ------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Move default-attribute reflection out of the constructor         | ~1.19 kB (≈0)      | 1.2 kB        | **Custom Elements Spec compliance.** Constructors may not mutate attributes, so `document.createElement` on a class with `static props` threw `NotSupportedError` in real browsers. Defaults now reflect on first connect, and markup/SSR-provided attributes win. Pure code movement — no net size cost.                                                        |
| Safe prop cloning (functions/instances) + define-time validation | 1.31 kB (+0.12 kB) | 1.2 → 1.35 kB | **No more `DataCloneError`.** `structuredClone` of a function/class-instance default crashed construction. Defaults are now cloned per key (plain data deep-copied so instances don't share object/array state; non-cloneable values kept by reference), and a one-time warning names any default whose type can't reflect to an attribute. Limit raised to fit. |
| Derive prop types from defaults only; log type violations instead of throwing (+ `static strictProps` opt-in) | 1.33 kB (+0.02 kB) | 1.35 kB | **Loud, not fatal.** The proxy setter locked a prop's type on first write and threw on mismatch; inside `attributeChangedCallback` that `TypeError` vanished into `window.onerror` and silently skipped rendering. Types are now taken from `static props` defaults only (undeclared props stay untyped), and a declared-type violation is logged via `console.error` and skipped so `render()`/`onChanges()` still run. Teams wanting hard enforcement can set `static strictProps = true` to restore throwing. |
| Correct empty-string / removed attribute handling; drop native-setter writes | 1.33 kB (≈0) | 1.35 kB | **State no longer corrupts on common attribute changes.** `attr=""` coerced to boolean `true` (echoed as `attr="true"`); `removeAttribute` wrote `null` into the proxy and threw before `render()`/`onChanges()`; `deserialize('', 'number')` threw. `attributeChangedCallback` now keeps strings as-is (`''` stays `''`), resets removed attributes to the declared default, wraps `deserialize` so a malformed value falls back to the raw string instead of skipping render, and no longer writes vestigial `this[prop]` fields that clobbered native setters like `title`/`id`/`lang`. Logic swap — no net size cost. |
| `onChanges` gains a clear attribute-vs-property distinction (**breaking**) | 1.34 kB (+0.01 kB) | 1.35 kB | **Self-documenting change payload.** `onChanges` previously passed only `property`, holding the kebab-case _attribute_ name — confusing in a library where `props` are camelCase. `property` now holds the camelCase _prop_ key (matching `this.props` access) and the kebab attribute name moves to a new `attribute` field. Handlers can read `this.props[property]` directly without re-deriving the key. **Breaking:** code reading `changes.property` for the attribute name must switch to `changes.attribute` (see the migration note on the life-cycle-hooks docs page). |
| Buffer attribute-driven render/onChanges until after `onInit` | 1.35 kB (+0.01 kB) | 1.35 kB | **`onInit` is guaranteed to run first.** Per spec, authored attributes fire `attributeChangedCallback` (→ `render`/`onChanges`) _before_ `connectedCallback`, so components that assume `onInit` already ran break in real browsers (happy-dom hides this). A `#connected` flag now buffers the `render`/`onChanges` side effects until after `onInit`, while the prop value is still applied immediately so `props` is correct inside `onInit`. Pre-connect changes are reflected by the first render and not replayed through `onChanges`. |