Merge pull request #1977 from isiahmeadows/remove-legacy-state

Remove support for `vnode.state = ...`

docs/change-log.md

@@ -18,6 +18,7 @@
 
 - API: `m.redraw()` is always asynchronous ([#1592](https://github.com/MithrilJS/mithril.js/pull/1592))
 - API: `m.mount()` will only render its own root when called, it will not trigger a `redraw()` ([#1592](https://github.com/MithrilJS/mithril.js/pull/1592))
+- API: Assigning to `vnode.state` (as in `vnode.state = ...`) is no longer supported. Instead, an error is thrown if `vnode.state` changes upon the invocation of a lifecycle hook.
 
 #### News
 

docs/vnodes.md

@@ -74,7 +74,6 @@ Property   | Type                             | Description
 `dom`      | `Element?`                       | Points to the element that corresponds to the vnode. This property is `undefined` in the `oninit` lifecycle method. In fragments and trusted HTML vnodes, `dom` points to the first element in the range.
 `domSize`  | `Number?`                        | This is only set in fragment and trusted HTML vnodes, and it's `undefined` in all other vnode types. It defines the number of DOM elements that the vnode represents (starting from the element referenced by the `dom` property).
 `state`    | `Object?`                        | An object that is persisted between redraws. It is provided by the core engine when needed. In POJO component vnodes, the `state` inherits prototypically from the component object/class. In class component vnodes it is an instance of the class. In closure components it is the object returned by the closure.
-`_state`   | `Object?`                        | For components, a reference to the original `vnode.state` object, used to lookup the `view` and hooks. This property is only used internally by Mithril, do not use or modify it.
 `events`   | `Object?`                        | An object that is persisted between redraws and that stores event handlers so that they can be removed using the DOM API. The `events` property is `undefined` if there are no event handlers defined. This property is only used internally by Mithril, do not use or modify it.
 `instance` | `Object?`                        | For components, a storage location for the value returned by the `view`. This property is only used internally by Mithril, do not use or modify it.
 `skip`     | `Boolean`                        | This property is only used internally by Mithril when diffing keyed lists, do not use or modify it.
@@ -89,7 +88,7 @@ The `tag` property of a vnode determines its type. There are five vnode types:
 Vnode type   | Example                        | Description
 ------------ | ------------------------------ | ---
 Element      | `{tag: "div"}`                 | Represents a DOM element.
-Fragment     | `{tag: "[", children: []}`     | Represents a list of DOM elements whose parent DOM element may also contain other elements that are not in the fragment. When using the [`m()`](hyperscript.md) helper function, fragment vnodes can only be created by nesting arrays into the `children` parameter of `m()`. `m("[")` does not create a valid vnode. 
+Fragment     | `{tag: "[", children: []}`     | Represents a list of DOM elements whose parent DOM element may also contain other elements that are not in the fragment. When using the [`m()`](hyperscript.md) helper function, fragment vnodes can only be created by nesting arrays into the `children` parameter of `m()`. `m("[")` does not create a valid vnode.
 Text         | `{tag: "#", children: ""}`     | Represents a DOM text node.
 Trusted HTML | `{tag: "<", children: "<br>"}` | Represents a list of DOM elements from an HTML string.
 Component    | `{tag: ExampleComponent}`      | If `tag` is a Javascript object with a `view` method, the vnode represents the DOM generated by rendering the component.