React-View-Models

@bigab/react-view-models

formerly known as @bigab/can-react

Connect observable view-models to React presentational components to create auto rendering container components.

Install

ES6

import { connect } from '@bigab/react-view-models';

CommonJS

var connect = require("@bigab/react-view-models").connect;

Usage

save-button.js

import { connect } from '@bigab/react-view-models';
import Button from './button.jsx';
import DefineMap from 'can-define/map/';
import Item from '../models/items';

let items = Items.getList({ selected: true });

export const ViewModel = DefineMap.extend({
  text: {
    get() {
      return `Save ${items.length} items`;
    }
  },
  onClick() {
    items.saveAllItems();
  }
});

export default connect( ViewModel, Button );

API

connect( {ViewModel|mapToProps}, Component )

Connect a view-model class or mapToProps function to React presentational components

connect() takes 2 arguments. The first is either a mapToProps function, a function that will return an object that the component instance will receive as props, or a ViewModel constructor function, which is an extended can-define/map. The second argument is a Presentational Component constructor function (a.k.a. a class or just component in React). The connect() function returns a Container Component which can then be imported and used in any react component or render function as usual.

ViewModel {constructor function}

A DefineMap constructor function.

Every instance of the returned component will generate an instance of the viewModel and provide props to the connected component based on the serialized Map instance.

The ViewModel instance will be initialized with the props passed into the Container Component. Whenever the container component will receive new props, the props object is passed to the viewModels .set() method, which may in turn cause an observable change event, which will re-run the serialization process and provide the connected component new props, which may cause a new render.

Methods on the view model, and copied onto the serialized props object and bound to the viewModel, so that they may be used as callbacks for the connected component, while still being called with the correct context.

Example:

import { connect } from '@bigab/react-view-models';
import DefineMap from 'can-define/map/map';
import TodoComponent from 'components/todo.jsx';
import Todo from 'models/todo';

const ViewModel = DefineMap.extend({
  showOnlyCompleted: 'boolean',
  todos: {
    value: Todo.getList( { completed: this.showOnlyCompleted } ),
    serialize: true
  },
  addTodo(formValues) {
    new Todo(formValues).save()
  }
});

export default connect( ViewModel, TodoComponent );

mapToProps {function}

A function that receives props as an argument and returns props to be sent to the connected component. This mapTpProps function will be converted into a compute and any changes made to observable derived values within this function will re-run this function to calculate the new props and pass them into the connected component.

The mapToProps function has one parameter, ownProps, which are the props that would have normally been passed into this component instance, as defined by the owner template (JSX).

The return value of the mapToProps function will be an object, mapping the values to be used as props to the Presentational Components instance, and will be merged into the props the component would already be receiving from it’s owner in the template it is used in (MapToProps values will overwrite the props passed in through the template). Since React components should not really be expecting observables, it may be appropriate (though not required) to serialize any observables in the mapToProps function (using attr, serialize, .map and .reduce ) when computing the value. Expecting observables in your react code will reduce re-usability).

Since the Container Component doesn't produce DOM artifacts of it’s own, you won’t end up with any wrapper divs or anything to worry about, but in react-device-tools you will see the component with the name connected( MyComponent ) in the tree. The Container Component holds the “newly computed props” value as its state. That state will update whenever the component “receives new props” or the compute emits a “change” event, which will then pass props down into the connected component instance, possibly causing some parts to re-render.

Any user actions that should affect the state should be handled with callbacks on props (like onClick or onSelectNewCountry), and should be implemented in the MapToProps function as methods on the return value. The callback methods can be used to directly act on the observables.

Example:

import Todo from 'models/todo';

connect( ownProps => {
  return {
    todos: Todo.getList( { completed: ownProps.showOnlyCompleted } ),
    addTodo(formValues) {
      new Todo(formValues).save()
    }
  };
}, MyComponent ) ;

Component {react component}

Any react component, usually a presentational component

Common use cases when using a view model

Here are some examples that may come up when using a view-model that may not be obvious at first:

Transforming a prop before passing it down to a child component

Sometimes you want a prop that is set on your connected component to be set to the exact same prop key on the child component, but modified slightly before passing it down. Here's an example of that:

const ViewModel = DefineMap.extend({
  someProp: {
    set( newVal ) {
      return newVal.toUpperCase();
    }
  }
});

Not passing through all props to the child component by default

By default, any props passed into the connected component will be passed down into the child component, unless otherwise tampered with. You control which props get passed down by setting a serialize param on each property, a using the '*' key to set the default to false.

const ViewModel = DefineMap.extend({
  '*': {
    serialize: false
  },
  somePropToBePassedThrough: {
    type: 'any',
    serialize: true
  }
});

Calling a parents callback, while also doing something special in your view models callback

Sometimes, you still want to notify the connected components owner component that the state changed (by calling a callback), but only after or while doing something different within the view-model. In this case, you'll want to define the callback prop as a observable attribute with a getter, rather than a method, and use the lastSetVal argument to call the parent components callback.

const ViewModel = DefineMap.extend({
  onChange: {
    type: 'function',
    get( lastSetValue ) {
      return (ev) => {
        this.changeTheThing(ev.target);
        if ( lastSetValue ) {
          return lastSetValue(ev);
        }
      };
    },
    serialize: true
  }
});

This can be one of the tricker conceits of the current API, suggestions are welcome.

Contributing

Contributing

Running the tests

Tests can run in the browser by opening a webserver and visiting the src/test/test.html page. Automated tests that run the tests from the command line in Firefox can be run with

npm test

Why React-View-Models?

React-View-Models follows the pattern popularized by react-redux, and provide users with a connect() function for extending React Presentational Components into Container Components, by providing connect with either a mapToProps function or more commonly a ViewModel constructor function, which is an extended DefineMap class, along with a presentational component, just like react-redux does.

The ViewModel is an observable, and when any observable change happens to one of it's properties, or if new props get set on the Container Component, it will be serialized and sent into the connected component as props, forcing an update/render.

The mapToProps function will get converted to a compute, so when any observable read inside the compute emits a change (or if new props get set on the Container Component), it will update the wrapped/connected presentational component instance with new derived props.

By following the patterns established by react-redux, but avoiding the complexity of pure-functional programing, reducer composition, immutability, and the single store paradigm, we hope to offer a familiar, powerful, but far simpler solution to creating great backing data stores for your react app.

License

MIT