Universal Model for Svelte

Universal model is a model which can be used with any of following UI frameworks:

• Angular 2+ universal-model-angular
• React 16.8+ universal-model-react
• Svelte 3+
• Vue.js 3+ universal-model-vue

If you want to use multiple UI frameworks at the same time, you can use single model with universal-model library

Install

npm install --save universal-model-svelte

Prerequisites for universal-model-svelte

"svelte": "^3.0.0",

Clean UI Architecture

• Model-View-Controller (https://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller)
• User triggers actions by using view or controller
• Actions are part of model and they manipulate state that is stored
• Actions can use services to interact with external (backend) systems
• State changes trigger view updates
• Selectors select and calculate a transformed version of state that causes view updates
• Views contain NO business logic
• There can be multiple interchangeable views that use same part of model
• A new view can be created to represent model differently without any changes to model
• View technology can be changed without changes to the model

Clean UI Code directory layout

UI application is divided into UI components. Common UI components should be put into common directory. Each component can consist of subcomponents. Each component has a view and optionally controller and model. Model consists of actions, state and selectors. In large scale apps, model can contain sub-store. Application has one store which is composed of each components' state (or sub-stores)

- src
  |
  |- common
  |  |- component1
  |  |- component2
  |  .  |- component2_1
  |  .  .
  |  .  .
  |- componentA
  |- componentB
  |  |- componentB_1
  |  |- componentB_2
  |- componentC
  |  |-view
  |  .
  |  .
  |- componentN
  |  |- controller
  |  |- model
  |  |  |- actions
  |  |  |- services
  |  |  |- state
  |  |- view
  |- store

API

Common API (Angular/React/Svelte/Vue)

createSubState(subState);
const store = createStore(initialState, combineSelectors(selectors))

const state = store.getState();
const selectors = store.getSelectors();
const [state, selectors] = store.getStateAndSelectors();

Svelte specific API

const [componentAState] = useState(id, [state.componentAState]);
const [selector1, selector2] = useSelectors(id, [selectors.selector1, selectors.selector2]);

Detailed API documentation

API Examples

Create initial states

const initialComponentAState = {
  prop1: 0,
  prop2: 0
};

Create selectors

When using foreign state inside selectors, prefer creating foreign state selectors and accessing foreign state through them instead of directly accessing foreign state inside selector. This will ensure better encapsulation of component state.

const createComponentASelectors = <T extends State>() => ({
  selector1: (state: State) => state.componentAState.prop1  + state.componentAState.prop2
  selector2: (state: State) => {
    const { componentBSelector1, componentBSelector2 } = createComponentBSelectors<State>();
    return state.componentAState.prop1 + componentBSelector1(state) + componentBSelector2(state);
  }
});

Create and export store in store.ts:

combineSelectors() checks if there are duplicate keys in selectors and will throw an error telling which key was duplicated. By using combineSelectors you can keep your selector names short and only namespace them if needed.

const initialState = {
  componentAState: createSubState(initialComponentAState),
  componentBState: createSubState(initialComponentBState)
};

export type State = typeof initialState;

const componentAStateSelectors = createComponentAStateSelectors<State>();
const componentBStateSelectors = createComponentBStateSelectors<State>();

const selectors = combineSelectors<State, typeof componentAStateSelectors, typeof componentBStateSelectors>(
  componentAStateSelectors,
  componentBStateSelectors
);

export default createStore<State, typeof selectors>(initialState, selectors);

in large projects you should have sub-stores for components and these sub-store are combined together to a single store in store.js:

componentBSubStore.js

const initialComponentsBState = { 
  componentBState: createSubState(initialComponentBState),
  componentB_1State: createSubState(initialComponentB_1State),
  componentB_2State: createSubState(initialComponentB_2State),
};

const componentBStateSelectors = createComponentBStateSelectors<State>();
const componentB_1StateSelectors = createComponentB_1StateSelectors<State>();
const componentB_2StateSelectors = createComponentB_2StateSelectors<State>();

const componentsBStateSelectors = combineSelectors<State, typeof componentBStateSelectors, typeof componentB_1StateSelectors, typeof componentB_2StateSelectors>(
  componentBStateSelectors,
  componentB_1StateSelectors,
  componentB_2StateSelectors,
);

store.js

const initialState = {
  ...initialComponentsAState,
  ...initialComponentsBState,
  .
  ...initialComponentsNState
};
      
export type State = typeof initialState;
    
const selectors = combineSelectors<State, typeof componentsAStateSelectors, typeof componentsBStateSelectors, ... typeof componentsNSStateelectors>(
  componentsAStateSelectors,
  componentsBStateSelectors,
  .
  componentsNStateSelectors
);
    
export default createStore<State, typeof selectors>(initialState, selectors);

Access store in Actions

Don't modify other component's state directly inside action, but instead call other component's action. This will ensure encapsulation of component's own state.

export default function changeComponentAAndBState(newAValue, newBValue) {
  const { componentAState } = store.getState();
  componentAState.prop1 = newAValue;
  
  // BAD
  const { componentBState } = store.getState();
  componentBState.prop1 = newBValue;
  
  // GOOD
  changeComponentBState(newBValue);
}

**Use actions, state and selectors in Views **

Components should use only their own state and access other components' states using selectors provided by those components. This will ensure encapsulation of each component's state.

<script>  
  const [componentAState] = useState('componentA', [store.getState().componentAState]);
  const selectors = store.getSelectors();
  const [selector1, selector2] = useSelectors('componentA', [selectors.selector1, selectors.selector2]);    
</script>

<div>
  {$componentAState.prop1}
  {$selector1} ...
<div>

You can also use state getters

<script>  
  const state = store.getState();
  const [componentAState, componentBStateProp1] = useState('componentA', [state.componentAState, () => state.componentAState.prop1]);
  const selectors = store.getSelectors();
  const [selector1, selector2] = useSelectors('componentA', [selectors.selector1, selectors.selector2]);    
</script>

<div>
  {$componentAState.prop1}
  {$componentBStateProp1} ...
<div>

Example

View

App.svelte

<script>
  import HeaderView from '@/header/HeaderView.svelte';
  import TodoListView from '@/todolist/TodoListView.svelte';
</script>

<div>
  <HeaderView />
  <TodoListView />
</div>

Header.svelte

<script>
  import changeUserName from '@/header/model/actions/changeUserName';
  import store from '@/store/store';

  const [headerText] = store.useSelectors('header', [store.getSelectors().headerText]);
</script>

<div>
  <h1>{$headerText}</h1>
  <label for="userName">User name:</label>
  <input id="userName" on:change="{(e) => changeUserName(e.target.value)}" />
</div>

TodoList.svelte

<script>
  import { onDestroy, onMount } from 'svelte';
  import store from '@/store/store';
  import fetchTodos from '@/todolist/model/actions/fetchTodos';
  import todoListController from '@/todolist/controller/todoListController';
  import toggleShouldShowOnlyUnDoneTodos from '@/todolist/model/actions/toggleShouldShowOnlyUnDoneTodos';
  import toggleIsDoneTodo from '@/todolist/model/actions/toggleIsDoneTodo';
  import removeTodo from '@/todolist/model/actions/removeTodo';

  const [todosState] = store.useState('todos', [store.getState().todosState]);
  const selectors = store.getSelectors();
  const [shownTodos, userName] = store.useSelectors('todos', [selectors.shownTodos, selectors.userName]);

  onMount(() => {
    // noinspection JSIgnoredPromiseFromCall
    fetchTodos();
    document.addEventListener('keydown', todoListController.handleKeyDown);
  });

  onDestroy(() => {
    document.removeEventListener('keydown', todoListController.handleKeyDown);
  });
</script>

<div>
  <input
    id="shouldShowOnlyUnDoneTodos"
    type="checkbox"
    bind:checked="{$todosState.shouldShowOnlyUnDoneTodos}"
    on:click="{toggleShouldShowOnlyUnDoneTodos}" />
  <label for="shouldShowOnlyUnDoneTodos">Show only undone todos</label>
  {#if $todosState.isFetchingTodos}
    <div>Fetching todos...</div>
  {:else if $todosState.hasTodosFetchFailure}
    <div>Failed to fetch todos</div>
  {:else}
    <ul>
      {#each $shownTodos as todo}
        <li>
          <input
            id="{todo.name}"
            type="checkbox"
            bind:checked="{todo.isDone}"
            on:click="{() => toggleIsDoneTodo(todo)}" />
          <label for="{todo.name}">{$userName}: {todo.name}</label>
          <button on:click="{() => removeTodo(todo)}">Remove</button>
        </li>
      {/each}
    </ul>
  {/if}
</div>

Controller

todoListController.ts

import addTodo from "@/todolist/model/actions/addTodo";
import removeAllTodos from "@/todolist/model/actions/removeAllTodos";

export default {
  handleKeyDown(keyboardEvent: KeyboardEvent): void {
    if (keyboardEvent.code === 'KeyA' && keyboardEvent.ctrlKey) {
      keyboardEvent.stopPropagation();
      keyboardEvent.preventDefault();
      addTodo();
    } else if (keyboardEvent.code === 'KeyR' && keyboardEvent.ctrlKey) {
      keyboardEvent.stopPropagation();
      keyboardEvent.preventDefault();
      removeAllTodos();
    }
  }
};

Model

Store

store.ts

import { combineSelectors, createStore, createSubState } from 'universal-model-svelte';
import initialHeaderState from '@/header/model/state/initialHeaderState';
import initialTodoListState from '@/todolist/model/state/initialTodosState';
import createTodoListStateSelectors from '@/todolist/model/state/createTodoListStateSelectors';
import createHeaderStateSelectors from '@/header/model/state/createHeaderStateSelectors';

const initialState = {
headerState: createSubState(initialHeaderState),
todosState: createSubState(initialTodoListState)
};

export type State = typeof initialState;
 
const headerStateSelectors =  createHeaderStateSelectors<State>();
const todoListStateSelectors = createTodoListStateSelectors<State>();

const selectors = combineSelectors<State, typeof headerStateSelectors, typeof todoListStateSelectors>(
 headerStateSelectors,
 todoListStateSelectors 
);

export default createStore<State, typeof selectors>(initialState, selectors);

State

Initial state

initialHeaderState.ts

export default {
  userName: 'John'
};

initialTodoListState.ts

export interface Todo {
  id: number,
  name: string;
  isDone: boolean;
}

export default {
  todos: [] as Todo[],
  shouldShowOnlyUnDoneTodos: false,
  isFetchingTodos: false,
  hasTodosFetchFailure: false
};

State selectors

createHeaderStateSelectors.ts

import { State } from '@/store/store';

const createHeaderStateSelectors = <T extends State>() => ({
  userName: (state: T) => state.headerState.userName,
  headerText: (state: T) => {
    const {
      todoCount: selectTodoCount,
      unDoneTodoCount: selectUnDoneTodoCount
    } = createTodoListStateSelectors<State>();
  
    return `${state.headerState.userName} (${selectUnDoneTodoCount(state)}/${selectTodoCount(state)})`;
  }
});

export default createHeaderStateSelectors;

createTodoListStateSelectors.ts

import { State } from '@/store/store';
import { Todo } from '@/todolist/model/state/initialTodoListState';

const createTodoListStateSelectors = <T extends State>() => ({
  shownTodos: (state: T) =>
    state.todosState.todos.filter(
      (todo: Todo) =>
        (state.todosState.shouldShowOnlyUnDoneTodos && !todo.isDone) ||
        !state.todosState.shouldShowOnlyUnDoneTodos
    ),
    todoCount: (state: T) => state.todosState.todos.length,
    unDoneTodoCount: (state: T) => state.todosState.todos.filter((todo: Todo) => !todo.isDone).length
});

export default createTodoListStateSelectors;

Service

ITodoService.ts

import { Todo } from '@/todolist/model/state/initialTodoListState';

export interface ITodoService {
  tryFetchTodos(): Promise<Todo[]>;
}

FakeTodoService.ts

import { ITodoService } from '@/todolist/model/services/ITodoService';
import { Todo } from '@/todolist/model/state/initialTodoListState';
import Constants from '@/Constants';

export default class FakeTodoService implements ITodoService {
  tryFetchTodos(): Promise<Todo[]> {
    return new Promise<Todo[]>((resolve: (todo: Todo[]) => void, reject: () => void) => {
      setTimeout(() => {
        if (Math.random() < 0.95) {
          resolve([
            { id: 1, name: 'first todo', isDone: true },
            { id: 2, name: 'second todo', isDone: false }
          ]);
        } else {
          reject();
        }
      }, Constants.FAKE_SERVICE_LATENCY_IN_MILLIS);
    });
  }
}

todoService.ts

import FakeTodoService from "@/todolist/model/services/FakeTodoService";

export default new FakeTodoService();

Actions

changeUserName.ts

import store from '@/store/store';

export default function changeUserName(newUserName: string): void {
  const { headerState } = store.getState();
  headerState.userName = newUserName;
}

addTodo.ts

import store from '@/store/store';

let id = 3;

export default function addTodo(): void {
  const { todosState } = store.getState();
  todosState.todos.push({ id, name: 'new todo', isDone: false });
  id++;
}

removeTodo.ts

import store from '@/store/store';
import { Todo } from '@/todolist/model/state/initialTodoListState';

export default function removeTodo(todoToRemove: Todo): void {
  const { todosState } = store.getState();
  todosState.todos = todosState.todos.filter((todo: Todo) => todo !== todoToRemove);
}

removeAllTodos.ts

import store from '@/store/store';

export default function removeAllTodos(): void {
  const { todosState } = store.getState();
  todosState.todos = [];
}

toggleIsDoneTodo.ts

import { Todo } from '@/todolist/model/state/initialTodoListState';

export default function toggleIsDoneTodo(todo: Todo): void {
  todo.isDone = !todo.isDone;
}

toggleShouldShowOnlyUnDoneTodos.ts

import store from '@/store/store';

export default function toggleShouldShowOnlyUnDoneTodos(): void {
  const { todosState } = store.getState();
  todosState.shouldShowOnlyUnDoneTodos = !todosState.shouldShowOnlyUnDoneTodos;
}

fetchTodos.ts

import store from '@/store/store';
import todoService from '@/todolist/model/services/todoService';

export default async function fetchTodos(): Promise<void> {
  const { todosState } = store.getState();

  todosState.isFetchingTodos = true;
  todosState.hasTodosFetchFailure = false;

  try {
    todosState.todos = await todoService.tryFetchTodos();
  } catch (error) {
    todosState.hasTodosFetchFailure = true;
  }

  todosState.isFetchingTodos = false;
}

Full Examples

https://github.com/universal-model/universal-model-svelte-todo-app

https://github.com/universal-model/universal-model-react-todos-and-notes-app

Dependency injection

If you would like to use dependency injection (noicejs) in your app, check out this example, where DI is used to create services.

Donate/Sponsor

If you would like to help me to develop more great stuff, you can donate or sponsor. Thank you!

License

MIT License