Package with React component wrapper for combining React with MobX.
Exports the observer decorator and some development utilities.
For documentation, see the MobX project.
This package supports both React and React Native.
npm install mobx-react --save
Or CDN: https://unpkg.com/mobx-react (namespace: mobxReact)
import { observer } from "mobx-react"
// - or, for custom renderers without DOM: -
import { observer } from "mobx-react/custom"This package provides the bindings for MobX and React. See the official documentation for how to get started.
- Minimal MobX, React, ES6, JSX, Hot reloading: MobX-React-Boilerplate
- TodoMVC MobX, React, ES6, JSX, Hot reloading: MobX-React-TodoMVC
- Minimal MobX, React, Typescript, TSX: MobX-React-Typescript-Boilerplate
- Minimal MobX, React, ES6(babel), JSPM with hot reloading modules: jspm-react
- React Native Counter: Mobx-React-Native-Counter
Function (and decorator) that converts a React component definition, React component class or stand-alone render function into a reactive component, which tracks which observables are used by render and automatically re-renders the component when one of these values changes.
See the MobX documentation for more details.
import { observer } from "mobx-react"
// ---- ES5 syntax ----
const TodoView = observer(
React.createClass({
displayName: "TodoView",
render() {
return <div>{this.props.todo.title}</div>
}
})
)
// ---- ES6 syntax ----
const TodoView = observer(
class TodoView extends React.Component {
render() {
return <div>{this.props.todo.title}</div>
}
}
)
// ---- ESNext syntax with decorators ----
@observer
class TodoView extends React.Component {
render() {
return <div>{this.props.todo.title}</div>
}
}
// ---- or just use a stateless component function: ----
const TodoView = observer(({ todo }) => <div>{todo.title}</div>)Observer is a React component, which applies observer to an anonymous region in your component.
It takes as children a single, argumentless function which should return exactly one React component.
The rendering in the function will be tracked and automatically re-rendered when needed.
This can come in handy when needing to pass render function to external components (for example the React Native listview), or if you
dislike the observer decorator / function.
class App extends React.Component {
render() {
return (
<div>
{this.props.person.name}
<Observer>{() => <div>{this.props.person.name}</div>}</Observer>
</div>
)
}
}
const person = observable({ name: "John" })
React.render(<App person={person} />, document.body)
person.name = "Mike" // will cause the Observer region to re-renderIn case you are a fan of render props, you can use that instead of children. Be advised, that you cannot use both approaches at once, children have a precedence. Example
class App extends React.Component {
render() {
return (
<div>
{this.props.person.name}
<Observer render={() => <div>{this.props.person.name}</div>} />
</div>
)
}
}
const person = observable({ name: "John" })
React.render(<App person={person} />, document.body)
person.name = "Mike" // will cause the Observer region to re-renderIf a component throws an error, this logs to the console but does not 'crash' the app, so it might go unnoticed.
For this reason it is possible to attach a global error handler using onError to intercept any error thrown in the render of an observer component.
This can be used to hook up any client side error collection system.
import { onError } from "mobx-react"
onError(error => {
console.log(error)
})When using server side rendering, normal lifecycle hooks of React components are not fired, as the components are rendered only once.
Since components are never unmounted, observer components would in this case leak memory when being rendered server side.
To avoid leaking memory, call useStaticRendering(true) when using server side rendering. This makes sure the component won't try to react to any future data changes.
The simple rule of thumb is: all components that render observable data. If you don't want to mark a component as observer, for example to reduce the dependencies of a generic component package, make sure you only pass it plain data.
Decorators are currently a stage-2 ESNext feature. How to enable them is documented here.
See this thread.
TL;DR: the conceptual distinction makes a lot of sense when using MobX as well, but use observer on all components.
When using @observer on a component, don't implement shouldComponentUpdate, as it will override the default implementation that MobX provides.
When using mobx-react, you should in general not need to write an sCU (in our entire Mendix code base we have none). If you really need to implement sCU, split the component into two, a reactive and non-reactive (with the sCU) part, or use <Observer> sections instead of observer on the entire component.
Similarly, PureComponent should not be combined with observer. As pure components are supposed to be dumb and never update themselves automatically, but only by getting passed in new props from the parent. observer is the opposite, it makes components smart and dependency aware, allowing them to update without the parents even needing to be aware of the change.
React components usually render on a fresh stack, so that makes it often hard to figure out what caused a component to re-render.
When using mobx-react you can define a new life cycle hook, componentWillReact (pun intended) that will be triggered when a component is scheduled to be re-rendered because
data it observes has changed. This makes it easy to trace renders back to the action that caused the rendering.
import { observer } from "mobx-react"
@observer
class TodoView extends React.Component {
componentWillReact() {
console.log("I will re-render, since the todo has changed!")
}
render() {
return <div>{this.props.todo.title}</div>
}
}componentWillReactdoesn't take argumentscomponentWillReactwon't fire before the initial render (usecomponentWillMountinstead)
MobX-react provides the following additional PropTypes which can be used to validate against MobX structures:
observableArrayobservableArrayOf(React.PropTypes.number)observableMapobservableObjectarrayOrObservableArrayarrayOrObservableArrayOf(React.PropTypes.number)objectOrObservableObject
Use import { PropTypes } from "mobx-react" to import them, then use for example PropTypes.observableArray
Provider is a component that can pass stores (or other stuff) using React's context mechanism to child components.
This is useful if you have things that you don't want to pass through multiple layers of components explicitly.
inject can be used to pick up those stores. It is a higher order component that takes a list of strings and makes those stores available to the wrapped component.
Example (based on the official context docs):
@inject("color")
@observer
class Button extends React.Component {
render() {
return <button style={{ background: this.props.color }}>{this.props.children}</button>
}
}
class Message extends React.Component {
render() {
return (
<div>
{this.props.text} <Button>Delete</Button>
</div>
)
}
}
class MessageList extends React.Component {
render() {
const children = this.props.messages.map(message => <Message text={message.text} />)
return (
<Provider color="red">
<div>{children}</div>
</Provider>
)
}
}Notes:
- If a component asks for a store and receives a store via a property with the same name, the property takes precedence. Use this to your advantage when testing!
- If updates to an observable store are not triggering
render(), make sure you are using Class methods for React lifecycle hooks such ascomponentWillMount() {}, usingcomponentWillMount = () => {}will create a property on the instance and cause conflicts with mobx-react. - Values provided through
Providershould be final, to avoid issues like mentioned in React #2517 and React #3973, where optimizations might stop the propagation of new context. Instead, make sure that if you put things incontextthat might change over time, that they are@observableor provide some other means to listen to changes, like callbacks. However, if your stores will change over time, like an observable value of another store, MobX will warn you. To suppress that warning explicitly, you can usesuppressChangedStoreWarning={true}as a prop at your own risk. - When using both
@injectand@observer, make sure to apply them in the correct order:observershould be the inner decorator,injectthe outer. There might be additional decorators in between. - The original component wrapped by
injectis available as thewrappedComponentproperty of the created higher order component. - For mounted component instances, the wrapped component instance is available through the
wrappedInstanceproperty (except for stateless components).
The above example in ES5 would start like:
var Button = inject("color")(
observer(
React.createClass({
/* ... etc ... */
})
)
)A functional stateless component would look like:
var Button = inject("color")(
observer(({ color }) => {
/* ... etc ... */
})
)Instead of passing a list of store names, it is also possible to create a custom mapper function and pass it to inject. The mapper function receives all stores as argument, the properties with which the components are invoked and the context, and should produce a new set of properties, that are mapped into the original:
mapperFunction: (allStores, props, context) => additionalProps
Since version 4.0 the mapperFunction itself is tracked as well, so it is possible to do things like:
const NameDisplayer = ({ name }) => <h1>{name}</h1>
const UserNameDisplayer = inject(stores => ({
name: stores.userStore.name
}))(NameDisplayer)
const user = mobx.observable({
name: "Noa"
})
const App = () => (
<Provider userStore={user}>
<UserNameDisplayer />
</Provider>
)
ReactDOM.render(<App />, document.body)N.B. note that in this specific case neither NameDisplayer nor UserNameDisplayer needs to be decorated with observer, since the observable dereferencing is done in the mapper function
Inject wraps a new component around the component you pass into it. This means that assigning a static property to the resulting component, will be applied to the HoC, and not to the original component. So if you take the following example:
const UserName = inject("userStore")(({ userStore, bold }) => someRendering())
UserName.propTypes = {
bold: PropTypes.boolean.isRequired,
userStore: PropTypes.object.isRequired // will always fail
}The above propTypes are incorrect, bold needs to be provided by the caller of the UserName component and is checked by React.
However, userStore does not need to be required! Although it is required for the original stateless function component, it is not
required for the resulting inject component. After all, the whole point of that component is to provide that userStore itself.
So if you want to make assertions on the data that is being injected (either stores or data resulting from a mapper function), the propTypes
should be defined on the wrapped component. Which is available through the static property wrappedComponent on the inject component:
const UserName = inject("userStore")(({ userStore, bold }) => someRendering())
UserName.propTypes = {
bold: PropTypes.boolean.isRequired // could be defined either here ...
}
UserName.wrappedComponent.propTypes = {
// ... or here
userStore: PropTypes.object.isRequired // correct
}The same principle applies to defaultProps and other static React properties.
Note that it is not allowed to redefine contextTypes on inject components (but is possible to define it on wrappedComponent)
Finally, mobx-react will automatically move non React related static properties from wrappedComponent to the inject component so that all static fields are
actually available to the outside world without needing .wrappedComponent.
inject also accepts a function ((allStores, nextProps, nextContext) => additionalProps) that can be used to pick all the desired stores from the available stores like this.
The additionalProps will be merged into the original nextProps before being provided to the next component.
import { IUserStore } from "myStore"
@inject(allStores => ({
userStore: allStores.userStore as IUserStore
}))
class MyComponent extends React.Component<{ userStore?: IUserStore; otherProp: number }, {}> {
/* etc */
}Make sure to mark userStore as an optional property. It should not (necessarily) be passed in by parent components at all!
Note: If you have strict null checking enabled, you could muffle the nullable type by using the ! operator:
public render() {
const {a, b} = this.store!
// ...
}
Currently, there is a community-discussion around the best way to use inject with Flow. Join the discussion at this gist.
It is allowed to pass any declared store in directly as a property as well. This makes it easy to set up individual component tests without a provider.
So if you have in your app something like:
<Provider profile={profile}>
<Person age={"30"} />
</Provider>In your test you can easily test the Person component by passing the necessary store as prop directly:
const profile = new Profile()
const mountedComponent = mount(
<Person age={'30'} profile={profile} />
)
Bear in mind that using shallow rendering won't provide any useful results when testing injected components; only the injector will be rendered.
To test with shallow rendering, instantiate the wrappedComponent instead: shallow(<Person.wrappedComponent />)
Should I use observer for each component?
You should use observer on every component that displays observable data.
Even the small ones. observer allows components to render independently from their parent and in general this means that
the more you use observer, the better the performance become.
The overhead of observer itself is neglectable.
See also Do child components need @observer?
I see React warnings about forceUpdate / setState from React
The following warning will appear if you trigger a re-rendering between instantiating and rendering a component:
Warning: forceUpdate(...): Cannot update during an existing state transition (such as within `render`). Render methods should be a pure function of props and state.`
-- or --
Warning: setState(...): Cannot update during an existing state transition (such as within `render` or another component's constructor). Render methods should be a pure function of props and state; constructor side-effects are an anti-pattern, but can be moved to `componentWillMount`.
Usually this means that (another) component is trying to modify observables used by this components in their constructor or getInitialState methods.
This violates the React Lifecycle, componentWillMount should be used instead if state needs to be modified before mounting.
Enables the tracking from components. Each rendered reactive component will be added to the componentByNodeRegistery and its renderings will be reported through the renderReporter event emitter.
Event emitter that reports render timings and component destructions. Only available after invoking trackComponents().
New listeners can be added through renderReporter.on(function(data) { /* */ }).
Data will have one of the following formats:
{
event: 'render',
renderTime: /* time spend in the .render function of a component, in ms. */,
totalTime: /* time between starting a .render and flushing the changes to the DOM, in ms. */,
component: /* component instance */,
node: /* DOM node */
}{
event: 'destroy',
component: /* component instance */,
node: /* DOM Node */
}WeakMap. Its get function returns the associated reactive component of the given node. The node needs to be precisely the root node of the component.
This map is only available after invoking trackComponents.