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Introduction to the "React" layer

Some admin modules render their UI with React, a popular Javascript library created by Facebook. For these sections, rendering happens via client side scripts that create and inject HTML declaratively using data structures.

There are some several members of this ecosystem that all work together to provide a dyanamic UI. They include:

  • ReactJS - A Javascript UI library
  • Redux - A state manager for Javascript
  • GraphQL - A query language for your API
  • Apollo - A framework for using GraphQL in your application

All of these pillars of the frontend application can be customised, giving you more control over how the admin interface looks, feels, and behaves.

First, a brief summary of what each of these are:

React

React's job is to render UI. Its UI elements are known as "components" and represent the fundamental building block of a React-rendered interface. A React component expressed like this:

<PhotoItem size={200} caption="Angkor Wat" onSelect={openLightbox}>
    <img src="path/to/image.jpg" />
</PhotoItem>

Might actually render HTML that looks like this:

<div class="photo-item">
    <div class="photo" style="width:200px;height:200px;">
        <img src="path/to/image.jpg">
    </div>
    <div class="photo-caption">
        <h3><a>Angkor Wat/a></h3>
    </div>
</div>

This syntax is known as JSX. It is transpiled at build time into native Javascript calls to the React API. While optional, it is recommended to express components this way.

The React Dev Tools extension available for Chrome and Firefox is critical to debugging a React UI. It will let you browse the React UI much like the DOM, showing the tree of rendered components and their current props and state in real time.

Redux

Redux is a state management tool with a tiny API that affords the developer highly predictable behaviour. All of the application state is stored in a single object, and the only way to mutate that object is by calling an action, which is just a simple object that describes what happened. A function known as a reducer mutates the state based on that action and returns a new reference with the updated state.

The following example is taken from the Redux Github page:

// reducer
function counter(state = 0, action) {
  switch (action.type) {
  case 'INCREMENT':
    return state + 1
  case 'DECREMENT':
    return state - 1
  default:
    return state
  }
}

let store = createStore(counter)
store.subscribe(() =>
  console.log(store.getState())
)
// Call an action
store.dispatch({ type: 'INCREMENT' })
// 1

It's important to be able to view the state of the React application when you're debugging and building the interface.

To be able to view the state, you'll need to be in a dev environment and have the Redux Devtools installed on Google Chrome or Firefox, which can be found by searching with your favourite search engine.

GraphQL and Apollo

GraphQL is a strictly-typed query language that allows you to describe what data you want to fetch from your API. Because it is based on types, it is self-documenting and predictable. Further, it's structure lends itself nicely to fetching nested objects. Here is an example of a simple GraphQL query:

query GetUser($ID: Int!) {
    user {
        name
        email
        blogPosts {
            title
            comments(Limit: 5) {
                author
                comment
            }
        }

    }
}

The above query is almost self-descriptive. It gets a user by ID, returns his or her name and email address, along with the title of any blog posts he or she has written, and the first five comments for each of those. The result of that query is, very predictably, JSON that takes on the same structure.

{
    "user": {
        "name": "Test user",
        "email": "[email protected]",
        "blogPosts": [
            {
                "title": "How to be awesome at GraphQL",
                "comments": [
                    {
                        "author": "Uncle Cheese",
                        "comment": "Nice stuff, bro"
                    }
                ]
            }
        ]
    }
}

On its own, GraphQL offers nothing functional, as it's just a query language. You still need a service that will invoke queries and map their results to UI. For that, SilverStripe uses an implementation of Apollo that works with React.

For more information

This documentation will stop short of explaining React, Redux, and GraphQL/Apollo in-depth, as there is much better documentation available all over the web. We recommend:

The Injector API

Much like SilverStripe's Injector API in PHP, the client-side framework has its own implementation of dependency injection known as Injector. Using Injector, you can register new services, and transform existing services.

Injector is broken up into three sub-APIs:

  • Injector.component for React UI components
  • Injector.reducer for Redux state management
  • Injector.form for forms rendered via FormSchema.

The frontend Injector works a bit differently than its backend counterpart. Instead of overriding a service with your own implementation, you enhance an existing service with your own concerns. This pattern is known as middleware.

Middleware works a lot like a decorator. It doesn't alter the original API of the service, but it can augment it with new features and concerns. This has the inherent advantage of allowing all thidparty code to have an influence over the behaviour, state, and UI of a component.

A simple middleware example

Let's say you have an application that features error logging. By default, the error logging service simply outputs to console.error. But you want to customise it to send errors to a thirdparty service. For this, you could use middleware to augment the default functionality of the logger.

LoggingService.js

const LoggingService = (error) => console.error(error);

export default LoggingService;

Now, let's add some middleware to that service. The signature of middleware is:

(next) => (args) => next(args)

Where next() is the next customisation in the "chain" of middleware. Before invoking the next implementation, you can add whatever customisations you need. Here's how we would use middleware to enhance LoggingService.

import thirdPartyLogger from 'third-party-logger';
const addLoggingMiddleware = (next) => (error) => {
    if (error.type === LoggingService.CRITICAL) {
        thirdpartyLogger.send(error.message);
    }
    return next(error);
}

Then, we would create a new logging service that merges both implementations.

import LoggingService from './LoggingService';
import addLoggingMiddleware from './addLoggingMiddleware';

const MyNewLogger = addLoggingMiddleware(LoggingService);

We haven't overriden any functionality. LoggingService(error) will still invoke console.error, once all the middleware has run. But what if we did want to kill the original functionality?

import LoggingService from './LoggingService';
import thirdPartyLogger from 'third-party-logger';

const addLoggingMiddleware = (next) => (error) => {
    // Critical errors go to a thirdparty service
    if (error.type === LoggingService.CRITICAL) {
        thirdPartyLogger.send(error.message);
    }
    // Other errors get logged, but not to our thirdparty
    else if (error.type === LoggingService.ERROR) {
        next(error);
    } 
    // Minor errors are ignored
    else {
        // Do nothing!
    }
}

Registering new services to the Injector

If you've created a module using React, it's a good idea to afford other developers an API to enhance those components, forms, and state. To do that, simply register them with Injector.

my-public-module/js/main.js

import Injector from 'lib/Injector';

Injector.component.register('MyComponent', MyComponent);
Injector.reducer.register('myCustom', MyReducer);

Services can then be fetched using their respective .get() methods.

const MyComponent = Injector.component.get('MyComponent');

Because of the unique structure of the form middleware, you cannot register new services to Injector.form.

Overwriting components by calling register() multiple times for the same service name is discouraged, and will throw an error. Should you really need to do this, you can pass { force: true } as the third argument to the register() function.

Transforming services using middleware

Now that the services are registered, other developers can customise your services with Injector.transform().

someone-elses-module/js/main.js

Injector.transform(
    'my-transformation',
    (updater) => {
        updater.component('MyComponent', MyCustomComponent);
        updater.reducer('myCustom', MyCustomReducer);

    }
);

Much like the configuration layer, we need to specify a name for this transformation. This will help other modules negotiate their priority over the injector in relation to yours.

The second parameter of the transform argument is a callback which receives an updaterobject. It contains four functions: component(), reducer(), form.alterSchema() and form.addValidation(). We'll cover all of these in detail functions in detail further into the document, but briefly, these update functions allow you to mutate the DI container with a wrapper for the service. Remember, this function does not replace the service -- it enhances it with new functionality.

Helpful tip: Name your component middleware

Since multiple enhancements can be applied to the same component, it will be really useful for debugging purposes to reveal the names of each enhancement on the displayName of the component. This will really help you when viewing the rendered component tree in React Dev Tools. For this, you can use the third parameter of the updater.component function. It takes an arbitrary name for the enhancement you're applying. module-a/js/main.js

 (updater) => updater.component('TextField', CharacterCounter, 'CharacterCounter')

module-b/js/main.js

 (updater) => updater.component('TextField', TextLengthChecker, 'TextLengthChecker')

Controlling the order of transformations

Sometimes, it's critical to ensure that your customisation happens after another one has been executed. To afford you control over the ordering of transforms, Injector allows before and after attributes as metadata for the transformation.

my-module/js/main.js

Injector.transform(
    'my-transformation',
    (updater) => {
        updater.component('MyComponent', MyCustomComponent);
        updater.reducer('myCustom', MyCustomReducer);

    },
    { after: 'another-module' }
);

before and after also accept arrays of constraints.

Injector.transform(
  'my-transformation', 
  (updater) => updater.component('MyComponent', MyCustomComponent);
  { before: ['my-transformation', 'some-other-transformation'] }
);

Using the * flag

If you really want to be sure your customisation gets loaded first or last, you can use * as your before or after reference.

Injector.transform(
  'my-transformation', 
  (updater) => updater.component('MyComponent', FinalTransform),
  { after: '*' }
);

This flag can only be used once per transformation. The following are not allowed:

  • { before: ['*', 'something-else'] }
  • { after: '*', before: 'something-else' }

Injector context

Because so much of UI design depends on context, dependency injection in the frontend is not necessarily universal. Instead, services are fetched with context.

example:

const CalendarComponent = Injector.get('Calendar', 'AssetAdmin.FileEditForm.StartDate');

Likewise, services can be applied for specific contexts.

Injector.transform('my-transform', (updater) => {
    // Applies to all text fields in AssetAdmin
    updater.component('TextField.AssetAdmin', MyTextField);

    // Applies to all text fields in AssetAdmin editform
    updater.component('TextField.AssetAdmin.FileEditForm', MyTextField);

    // Applies to any textfield named "Title" in AssetAdmin
    updater.component('TextField.AssetAdmin.*.Title', MyTextField);

    // Applies to any textfield named "Title" in any admin
    updater.component('TextField.*.*.Title', MyTextField);
})

To apply context-based transformations, you'll need to know the context of the component you want to customise. To learn this, open your React Developer Tools (see above) window and inspect the component name. The context of the component is displayed between two square brackets, appended to the original name, for example: TextField[TextField.AssetAdmin.FileEditForm.Title]. The context description is hierarchical, starting with the most general category (in this case, "Admin") and working its way down to the most specific category (Name = 'Title'). You can use Injector to hook into the level of specificity that you want.

Customising React components with Injector

When middleware is used to customise a React component, it is known as a higher order component.

Using the PhotoItem example above, let's create a customised PhotoItem that allows a badge, perhaps indicating that it is new to the gallery.

const enhancedPhoto = (PhotoItem) => (props) => {
    const badge = props.isNew ? 
      <div className="badge">New!</div> : 
      null;

    return (
        <div>
            {badge}
            <PhotoItem {...props} />
        </div>
    );
}

const EnhancedPhotoItem = enhancedPhoto(PhotoItem);

<EnhancedPhotoItem isNew={true} size={300} />

Alternatively, this component could be expressed with an ES6 class, rather than a simple function.

const enhancedPhoto = (PhotoItem) => {
    return class EnhancedPhotoItem extends React.Component {
        render() {
            const badge = this.props.isNew ? 
              <div className="badge">New!</div> : 
              null;

            return (
                <div>
                    {badge}
                    <PhotoItem {...this.props} />
                </div>
            );

        }
    }
}

When components are stateless, using a simple function in lieu of a class is recommended.

Using dependencies within your React component

If your component has dependencies, you can add them via the injector using the inject() higher order component. The function accepts the following arguments:

inject([dependencies], mapDependenciesToProps)(Component)
  • [dependencies]: An array of dependencies (or a string, if just one)
  • mapDependenciesToProps: (optional) All dependencies are passed into this function as params. The function is expected to return a map of props to dependencies. If this parameter is not specified, the prop names and the service names will mirror each other.

The result is a function that is ready to apply to a component.

const MyInjectedComponent = inject(
  ['Dependency1', 'Dependency2']
)(MyComponent);
// MyComponent now has access to props.Dependency1 and props.Dependency2

Here is its usage with a bit more context:

my-module/js/components/Gallery.js

import React from 'react';
import { inject } from 'lib/Injector';

class Gallery extends React.Component 

{
  render() {
    const { SearchComponent, ItemComponent } = this.props;
    return (
      <div>  
         <SearchComponent />
        {this.props.items.map(item => (
          <ItemComponent title={item.title} image={item.image} />
        ))}
      </div>
    );
  }
}

export default inject(
  Gallery, 
  ['GalleryItem', 'SearchBar'], 
  (GalleryItem, SearchBar) => ({
    ItemComponent: GalleryItem,
    SearchComponent: SearchBar
  })
 );

Using the injector directly within your component

On rare occasions, you may just want direct access to the injector in your component. If your dependency requirements are dynamic, for example, you won't be able to explicitly declare them in inject(). In cases like this, use withInjector(). This higher order component puts the Injector instance in context.

class MyGallery extends React.Component 
{
  render () {
    <div>
      {this.props.items.map(item => {
        const Component = this.context.injector.get(item.type);
        return <Component title={item.title} image={item.image} />
      })}
    </div>
  }
}

export default withInjector(MyGallery);

Using Injector to customise forms

Forms in the React layer are built declaratively, using the FormSchema API. A component called FormBuilderLoader is given a URL to a form schema definition, and it populates itself with fields (both structural and data-containing) and actions to create the UI for the form. Each form is required to have an identifier property, which is used to create context for Injector when field components are fetched. This affords developers the opportunity provide very surgical customisations.

Updating the form schema

Most behavioural and aesthetic customisations will happen via a mutation of the form schema. For this, we'll use the updater.form.alterSchema() function.

Injector.transform(
    'my-custom-form',
    (updater) => {
        updater.form.alterSchema(
            'AssetAdmin.*',
            (form) =>
        form.updateField('Title', {
            myCustomProp: true
        })
        .getState()
        )
    }
);

The alterSchema() function takes a callback, with an instance of FormStateManager (form in the above example) as a parameter. FormStateMangaer allows you to declaratively update the form schema API using several helper methods, including:

  • updateField(fieldName:string, updates:object)
  • updateFields({ myFieldName: updates:object })
  • mutateField(fieldName:string, callback:function)
  • setFieldComponent(fieldName:string, componentName:string)
  • setFieldClass(fieldName:string, cssClassName:string, active:boolean)
  • addFieldClass(fieldName:string, cssClassName:string)
  • removeFieldClass(fieldName:string, cssClassName:string)

For a complete list of props that are available to update on a Field object, see http://redux-form.com/6.8.0/docs/api/Field.md/#props-you-can-pass-to-field-

It is critical that you end series of mutation calls with getState().

In addition to mutation methods, several readonly methods are available on FormSchemaManager to read the current form state, including:

  • getValues(): Returns a map of field names to their current values
  • getValue(fieldName:string): Returns the value of the given field
  • isDirty(): Returns true if the form has been mutated from its original state
  • isPristine(): Returns true if the form is in its original state
  • isValid(): Returns true if the form has no validation errors
  • isInvalid(): Returns true if the form has validation errors

Adding validation to a form

Validation for React-rendered forms is handled by the redux-form package. You can inject your own middleware to add custom validation rules using the updater.form.addValidation() function.

Injector.transform(
  'my-validation',
  (updater) => {
    updater.form.addValidation(
      'AssetAdmin.*',
      (values, validator) => {
          if (values.PostalCode.length !== 5) {
              validator.addError('PostalCode', 'Invalid postal code');
          }
      }
    )
  }
);

The addValidation() function takes a callback, with an instance of FormValidationManager (validator in the above example) as a parameter. FormValidationMangaer allows you to manage the validation result using several helper methods, including:

  • addError(fieldName:string, message:string)
  • addErrors(fieldName:string, messages:Array)
  • hasError(fieldName:string)
  • clearErrors(fieldName:string)
  • getErrors(fieldName:string)
  • reset(void)

Using Injector to customise Redux state data

Before starting this tutorial, you should become familiar with the concepts of Immutability and Redux.

The examples use Spread in object literals which is at this moment in Stage 3 Proposal. If you're more comfortable with using the Object.assign() API that shouldn't present any problems and should work the same.

For example:

  newProps = { ...oldProps, name: 'New name' };

is the same as

  newProps = Object.assign(
    {},
    oldProps,
    { name: 'New name' }
  );

To start customising, you'll need to transform an existing registered reducer, you can find what reducers are registered by importing Injector and running Injector.reducer.getAll()

Injector.transform('customisationName', (updater) => {
  updater.reducer('assetAdmin', MyReducerTransformer);
});

As you can see, we use the reducer() function on the update object to augment Redux state transformations.

Using Redux dev tools

It is important to learn the basics of Redux dev tools, so that you can find out what ACTIONS and payloads to intercept and modify in your Transformer should target.

Most importantly, it helps to understand the "Action" sub-tab on the right panel (bottom if your dev tools is small), as this will be the data your Transformer will most likely receive, pending other transformers that may run before/after your one.

Structuring a transformer

We use currying to supply utilities which your transformer may require to handle the transformation.

  • originalReducer - reducer callback which the transformer is customising, this will need to be called in most cases. This will also callback other transformations down the chain of execution. Not calling this will break the chain.
  • getGlobalState - A function that gets the state of the global Redux store. There may be data outside the current scope in the reducer which you may need to help determine the transformation.
  • state - current state of the current scope. This is what should be used to form the new state.
  • type - the action to fire, like in any reducer in Redux. This helps determine if your transformer should do anything.
  • payload - the new data sent with the action to mutate the Redux store.
const MyReducerTransformer = (originalReducer) => (globalState) => (state, { type, payload }) => {
  switch (type) {
    case 'EXISTING_ACTION': {
      // recommended to call and return the originalReducer with the payload changed by the transformer
      /* return action to call here; */
    }

    case 'OVERRIDE_EXISTING_ACTION': {
      // could omit the originalReducer to enforce your change or cancel the originalREducer's change
    }

    default: {
      // it is important to return the originalReducer with original redux parameters.
      return originalReducer(state, { type, payload });
    }
  }
}

A basic transformation

This example we will illustrate modifying the payload to get different data saved into the original reducer.

We will rename anything in the breadcrumbs that is displaying "Files" to display "Custom Files" instead.

const MyReducerTransformer = (originalReducer) => (getGlobalState) => (state, { type, payload }) => {
  switch (type) {
    case 'SET_BREADCRUMBS': {
      return originalReducer(state, {
        type,
        payload: {
          breadcrumbs: payload.breadcrumbs.map((crumb) => (
            (crumb.text === 'Files')
              ? { ...crumb, text: 'Custom Files' }
              : crumb
          )),
        },
      });
    }
  }
};

Using the globalState

Accessing the globalState is easy, as it is passed in as part of the curried functions definition.

export default (originalReducer) => (getGlobalState) => (state, { type, payload }) => {
  const baseUrl = globalState.config.baseUrl;

  switch (type) {
    /* ... cases here ... */
  }
}

Setting a different initial state

We can easily define a new initial state by providing the state param with a default value. It is recommended to keep the call for the original initialState for your initialState then override values, so that you do not lose any potentially critical data that would have originally been set.

const MyReducerTransformer = (originalReducer) => () => (state, { type, payload }) => {
  if (typeof state === 'undefined') {
    return {
      ...originalReducer(state, { type, payload }),
      myCustom: 'initial state here',
    };
  }
};

Cancelling an action

There are valid reasons to break the chain of reducer transformations, such as cancelling the Redux store update. However, like an original reducer in redux, you will still need to return the original state.

export default (originalReducer) => (getGlobalState) => (state, { type, payload }) => {
  switch (type) {
    case 'CANCEL_THIS_ACTION': {
      return state;
    }
  }
};

Calling a different action

You could manipulate the action called by the originalReducer, there isn't an example available but this block of code will present the theory of how it can be achieved.

 default (originalReducer) => (getGlobalState) => (state, { type, payload }) => {
  switch (type) {
    case 'REMOVE_ERROR': {
      // we'd like to archive errors instead of removing them
      return originalReducer(state, {
        type: 'ARCHIVE_ERROR',
        payload,
      });
    }
  }
};

Using Injector to customise GraphQL queries

(coming soon)

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