Web-Apps with Svelte

A Practical Introduction

The Trainer

 

  • Nils Röhrig

 

  • Software Engineer @ Loql

 

  • Frontend focus

 

  • Svelte user since 2019

 

  • Speaker at conferences and meetups

© volkerrenner.de

Agenda

Part II

- Nesting

- Props

- Component Slots

- Event Dispatching

- Event Forwarding

- Events vs. Callbacks

Part I

- Framework

- Local State

- Directives

- Control Structures

- CSS Support

- SVG Support

- Reactivity

Part III

- Svelte Stores

- Custom  Stores

- Svelte Context

- Stores in Context

Part IV

- Working with Promises

- Transitions

- Svelte Actions

- DOM References

Coffee Break
10:00 - 10:30

Lunch Break
12:00 - 13:00

Coffee Break
14:30 - 15:00

Agenda

Teil II

- Verschachtelung

- Props

- Komponenten- Slots

- Event Dispatching

- Event Forwarding

- Events oder Callbacks

Teil I

- Framework

- Lokaler State

- Direktiven

- Kontrollstrukturen

- CSS Support

- SVG Support

- Reaktivität

Teil III

- Svelte Stores

- Custom  Stores

- Svelte Kontext

- Stores im Kontext

Teil IV

- Arbeit mit Promises

- Transitionen

- Svelte Actions

- DOM-Referenzen

Kaffepause
10:30 - 11:00

Mittagspause
12:30 - 13:30

Kaffepause
15:00 - 15:30

Demo of the workshop app

Part I

Teil I

- Framework

- Local State

- Directives

- Control Structures

- CSS Support

- SVG Support

- Reactivity

Svelte is a tool for building web applications. Like other user interface frameworks, it allows you to build your app declaratively out of components that combine markup, styles and behaviours.

- Svelte Tutorial

Svelte is a component framework

Svelte is a component framework

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etc. pp...

Component

Component

Component

These components are compiled into small, efficient JavaScript modules that eliminate overhead traditionally associated with UI frameworks.

- Svelte Tutorial

Svelte is a compiler

Svelte is a compiler

<h1>Simple Component</h1>

Component.svelte

Svelte is a compiler

<h1>Simple Component</h1>

Svelte is a compiler

<h1>Simple Component</h1>

Svelte is a compiler

<h1>Simple Component</h1>
import { SvelteComponent, detach, element, init,
         insert, noop, safe_not_equal } from "svelte/internal";

function create_fragment(ctx) {
  let h1;

  return {
    c() {
      h1 = element("h1");
      h1.textContent = "Simple Component";
    },
    m(target, anchor) {
      insert(target, h1, anchor);
    },
    p: noop,
    i: noop,
    o: noop,
    d(detaching) {
      if (detaching) detach(h1);
    },
  };
}

class SimpleComponent extends SvelteComponent {
  constructor(options) {
    super();
    init(this, options, null, create_fragment, safe_not_equal, {});
  }
}

export default SimpleComponent;

Svelte is a compiler

<h1>Simple Component</h1>
import { [...] } from "svelte/internal";
function create_fragment(ctx) {
  let h1;  
  return {
    c() {
      h1 = element("h1");
      h1.textContent = "Simple Component";
    },
    m(target, anchor) {
      insert(target, h1, anchor);
    },
    p: noop, i: noop, o: noop,
    d(detaching) { if (detaching) detach(h1); },
  };
}
class Component extends SvelteComponent {
  constructor(options) {
    super();
    init(this, options, null, create_fragment, 
		safe_not_equal, {});
  }
}
export default Component;

Component.js

Svelte is a compiler

<h1>Simple Component</h1>
import Component from "./Component.js";

const app = new Component({
  target: document.body,
});

export default app;

main.js

Anatomy of a component

Anatomy of a component

<script>
  // STATE & BEHAVIOR
</script>

<!-- DECLARATIVE MARKUP -->
<h1>Hello enterJS!</h1>
<p>{"Put your JS expressions in curly braces."}</p>

<style>
  /* PRESENTATION */
</style>

Component.svelte

Local State

Local State

  • The local component state in Svelte consists of local variables.
     
  • It describes the state of the component and is not shared with other components.
     
  • The local state is reactive in the Svelte sense, meaning that only the affected parts of the component are updated when changes occur.

Local State Demo REPL

Directives

Directives

  • Svelte directives can be used as attributes in Svelte elements.
     
  • They can control the behavior of elements, such as binding data or handling events.
     
  • Svelte provides various directives that can control the behavior of elements, such as on: and bind:.

Directives Demo REPL

Control Structures

Control Structures

  • Control structures are an integral part of Svelte markup.
     
  • They control the program flow and are known from other programming languages.
     
  • Svelte provides a block syntax for control structures that supports various expressions like if, else, each, and others.

Control Structures Demo REPL

Changing the value of an {#each} block

Changing the value of an {#each} block

  • If the value of an {#each} block in Svelte is changed, elements are removed or added only at the end of the block.
     
  • Changed elements are updated at the same position in the DOM.
     
  • Using unique IDs can avoid unwanted effects if rendered elements are not directly or reactively dependent on the change of the value.

Keyed Each Block

Keyed Each Block Demo REPL

Local Constants

Local Constants Demo REPL

Reactivity

Reactivity

  • Svelte integrates reactivity as a core element.
     
  • The = operator and its variants are used in Svelte to establish data binding between variables and UI elements.
     
  • Svelte tracks dependencies between variables and only updates the parts of the DOM that are affected by them.
     
  • By tracking assignments at build time, the code is optimized.
     
  • Svelte provides language support such as Reactive Statements.

Reactivity Demo REPL

CSS Support

CSS Support

  • CSS is part of the Single-File-Component approach in Svelte.
     
  • Styles are automatically scoped to avoid conflicts.
     
  • Directives allow for binding of classes.
     
  • There are also directives for selectively setting individual CSS properties.

CSS Support Demo REPL

SVG Support

SVG Support

  • Svelte offers full support for SVG graphics.
     
  • SVG elements can be directly included in Svelte components.
     
  • Svelte allows for dynamically updating SVG attributes and properties.

SVG Support Demo REPL

Live Coding

Exercise

Exercise

  1. Add filters for transactions:
    • All time: All transactions
    • Monthly: Current month
    • Weekly: Current calendar week
  2. The filtering should be reflected in
    • the StatCards
    • the transaction table

 

Notes

  • The implementation method is freely selectable
  • Modules in src/lib can be used

Tasks

git checkout tags/part_1_exercise -b <BRANCH_NAME>

npm ci

npm run dev

Preparation

nilsroehrig/svelte-workshop-ijs-munich-2023

Repository

Proposed Solution

Part II

Part II

- Nesting

- Props

- Component Slots

- Event Dispatching

- Event Forwarding

- Events vs. Callbacks

Nesting of components

Nesting of components

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Nesting of components

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<Logo>

<Header>

<App>

<NavItem>

<NavItem>

<NavBar>

<Label>

<Input>

<Form>

<Button>

Component Nesting Demo REPL

Props

Props

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Props

<NavItem>

<NavItem>

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Props

<NavItem                          >

<NavItem                              >

label="Home"

label="Register"

Register
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Props

<script>
    const str = "a string";
    const num = 12345;
    const bool = true;
    const obj = {key: "value"};
    const arr = [1, 2, 3, 4, 5];
    
    function callback() {
        console.log("callback");
    }
</script>

<AnyComponent 
    stringProp={str}
    numberProp={num}
    booleanProp={bool}
    objectProp={obj}
    arrayProp={arr}
    {callback} 
/>

Props

<script>
    const str = "a string";
    const num = 12345;
    const bool = true;
    const obj = {key: "value"};
    const arr = [1, 2, 3, 4, 5];
    
    function callback() {
        console.log("callback");
    }
</script>

<AnyComponent 
    stringProp={str}
    numberProp={num}
    booleanProp={bool}
    objectProp={obj}
    arrayProp={arr}
    {callback} 
/>

<script>
  export let stringProp = "";
  export let numberProp = 0;
  export let booleanProp = true;
  export let objectProp = {key: "value"};
  export let arrayProp = [1, 2, 3];
  export let callback = () => undefined;
</script>

<p>{stringProp}</p>
<p>{numberProp}</p>
<p>{booleanProp}</p>

{#each Object.entries(objectProp) as [key, value]}
  <p>{key}: {value}</p>
{/each}

{#each arrayProp as value}
  <p>{value}</p>
{/each}

<button on:click={callback}>Call back</button>

Props Demo REPL

$$props & $$restProps

$$props & $$restProps Demo REPL

Event Dispatching

Event Dispatching

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Event Dispatching

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<App>

<Form>

Event Dispatching

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<App>

<Form>

How?

Event Dispatching

<script>
  import { createEventDispatcher } from 'svelte';
  const dispatch = createEventDispatcher();
  
  async function submitForm() {
    await postForm();
    dispatch("form:posted", { /* any information to share */ });
  }
</script>

<form on:submit={submitForm}>
  <!-- form content -->
</form>

Form.svelte

Event Dispatching

<script>
  import { createEventDispatcher } from 'svelte';
  const dispatch = createEventDispatcher();
  
  async function submitForm() {
    await postForm();
    dispatch("form:posted", { /* any information to share */ }
  }
</script>

<form on:submit={submitForm}>
  <!-- form content -->
</form>

Form.svelte

<script>
  import Form from './Form.svelte';
  
  function handleSubmit(event) {
    
    /* here the shared information can be found, 
     * as Svelte events are just instances of 
     * CustomEvent */
    const { detail } = event;
    console.log({detail});
  }
</script>

<Form on:form:posted={handleSubmit} />

App.svelte

Event Dispatching Demo REPL

Event Forwarding

Event Forwarding

  • Event forwarding forwards events from child components to parent components.
     
  • This allows parent components to react to user actions in their child components.
     
  • It promotes coordination of data and actions across the component hierarchy.

Event Forwarding

<script>
  import { createEventDispatcher } from 'svelte';
  const dispatch = createEventDispatcher();
  
  async function submitForm() {
    await postForm();
    dispatch("submit", { /* any information to share */ }
  }
</script>

<form on:submit={submitForm}>
  <!-- form content -->
</form>

Form.svelte

<script>
  import Form from './Form.svelte';
  
  function handleSubmit(event) {    
    /* here the shared information can be found, 
     * as Svelte events are just instances of 
     * CustomEvent */
    const { detail } = event;
    console.log({detail});
  }
</script>

<Form on:submit={handleSubmit} />

App.svelte

Event Forwarding

<script>
  import { createEventDispatcher } from 'svelte';
  const dispatch = createEventDispatcher();
  
  async function submitForm() {
    await postForm();
    dispatch("submit", { /* any information to share */ }
  }
</script>

<form on:submit={submitForm}>
  <!-- form content -->
</form>

Form.svelte

<script>
  import Form from './Form.svelte';
  
  function handleSubmit(event) {    
    /* here the shared information can be found, 
     * as Svelte events are just instances of 
     * CustomEvent */
    const { detail } = event;
    console.log({detail});
  }
</script>

<Form on:submit={handleSubmit} />

App.svelte

Event Forwarding

<script>
  import { createEventDispatcher } from 'svelte';
  const dispatch = createEventDispatcher();
  
  async function submitForm() {
    await postForm();
    dispatch("submit", { /* any information to share */ }
  }
</script>

<form on:submit={submitForm}>
  <!-- form content -->
</form>

Form.svelte

<script>
  import Form from './Form.svelte';
  
  function handleSubmit(event) {    
    /* here the shared information can be found, 
     * as Svelte events are just instances of 
     * CustomEvent */
    const { detail } = event;
    console.log({detail});
  }
</script>

<Form on:submit={handleSubmit} />

App.svelte

Event Forwarding

<form on:submit>
  <!-- form content -->
</form>

Form.svelte

<script>
  import Form from './Form.svelte';
  
  async function handleSubmit(event) {
    const data = new FormData(event.target);
    await postData(data);
  }
</script>

<Form on:submit={handleSubmit} />

App.svelte

Event Forwarding Demo REPL

Events vs. Callbacks

Events vs. Callbacks

<script>
  import AnotherComponent from './AnotherComponent.svelte';
  
  function callback() {
    console.log("I am a callback. Arguments: ", ...arguments);
  }
</script>

<AnotherComponent {callback} />
<script>
  export let callback;
</script>

<button on:click={callback}>
  Click me!
</button>

Component.svelte

AnotherComponent.svelte

Events vs. Callbacks

<script>
  import Button from './Button.svelte';
  
  function handleButtonElementClick() {
    console.log("Button element clicked.");
  }
  
  function handleButtonComponentClick() {
    console.log("Button component clicked.");
  }
</script>

<button on:click={handleButtonElementClick}>Button element</button>
<Button onClick={handleButtonComponentClick}>Button Component</Button>

Events vs. Callbacks Demo REPL

Component Slots

Component Slots

  • Slots in Svelte allow for the dynamic injection of content into components.
     
  • They are defined in components using the <slot> element.
     
  • Slot contents are provided by parent components.
     
  • Slot contents can contain any valid Svelte markup.

Component Slots

Dialog

Text that is shown in the dialog. Potentially expanded by further content.

Okay

Component Slots

<strong>Dialog</strong>

<p>Text that is shown in the dialog. Potentially expanded by further content.</p>

<button>Okay</button>

Component Slots Demo REPL

Live Coding

Exercise

Exercise

  1. Create a detail page for transactions
     
  2. The detail page should contain all information about a transaction
     
  3. On each detail page, the respective transaction can be deleted

 

Notes

  • The implementation method is freely selectable
     
  • The example app uses modified StatCards

Tasks

Repository

git checkout tags/part_2_exercise -b <BRANCH_NAME>

npm ci

npm run dev

Preparation

nilsroehrig/svelte-workshop-ijs-munich-2023

https://testing-library.com/docs/svelte-testing-library/intro/

Proposed Solution

Part III

Part III

- Svelte Stores

- Custom  Stores

- Svelte Context

- Stores in Context

Svelte Stores

Svelte Stores

  • Stores are JavaScript objects that encapsulate values and can be subscribed to using the .subscribe method.
     
  • Subscribers are notified of updates.
     
  • Svelte provides language support for using stores.
     
  • There are different types of built-in stores, namely readable, writable, and derived.

Language Support Demo REPL

Built-In Stores Demo REPL

Svelte Store Contract

Svelte Store Contract

  • A Store must contain a .subscribe method that accepts a subscription function as an argument to create a subscription.
     
  • The subscription function must be called immediately and synchronously with the current value of the Store when .subscribe is called.
     
  • All active subscription functions of the Store must be called synchronously later when the value of the Store changes.
     
  • .subscribe must return an unsubscribe function. Calling it must end the subscription and the corresponding subscription function must not be called again by the Store.
     
  • A store can optionally include a .set method, which accepts a new value as an argument and updates the store with it. Such a store is referred to as a writable store.

Custom Stores

Custom Store Demo REPL

Svelte Context

Svelte Context

  • The context is a key-value store that enables data transfer from a component to all of its hierarchically subordinate components without explicit props.
     
  • setContext() is used to create and provide the context in the parent component.
     
  • getContext() is used to retrieve the context in the child components.
     
  • The context can contain arbitrary values, such as configuration data, functions, or stores.
     
  • The context is not reactive in the Svelte sense.

Svelte Context Demo REPL

Stores in Context

Stores in Context Demo REPL

Live Coding

Exercise

Exercise

  1. Create a mechanism for synchronizing transactions in the browser's local storage


Notes

  • The type of implementation is up to you
     
  • Stores can be subscribed to

Tasks

Repository

git checkout tags/part_3_exercise -b <BRANCH_NAME>

npm ci

npm run dev

Preparation

nilsroehrig/svelte-workshop-ijs-munich-2023

Proposed Solution

Part IV

Part IV

- Working with Promises

- Transitions

- Svelte Actions

- DOM References

Working with Promises

Working with Promises

Render Component

Fetch Data

Update View

Arbeit mit Promises

Render Component

Fetch Data

Update View

Working with Promises Demo REPL

Transitions

Transitions

  • Transitions in Svelte allow for animated transitions when adding or removing DOM elements.
     
  • They are used through the transition directive and allow for the use of built-in or custom transitions.
     
  • Svelte already includes transition effects such as fade, slide, or scale.
     
  • Custom function effects follow a unified interface, which can be found in the Svelte documentation.

Transitionen

Transitions Demo REPL

Refs & Actions

Refs & Actions

  • Refs are a way to reference DOM elements.
     
  • They are created using the bind:this={variable} directive and can be used and shared like other variables.
     
  • Actions are functions that can be directly attached to DOM elements without creating an explicit reference.
     
  • They are used with the use:actionName={params} directive.
     
  • Actions are executed when added to the DOM.
     
  • They can optionally return a function that is executed when removed from the DOM.

Refs & Actions Demo REPL

Live Coding

Übung

Exercise

  1. Create a visualization for income and expenses using Chart.js


Notes

  • Chart.js is already listed in the dependencies
     
  • Use Svelte Actions to bring visualizations into the DOM
     
  • Chart type, implementation method, etc. are freely selectable

Tasks

Repository

git checkout tags/part_4_exercise -b <BRANCH_NAME>

npm ci

npm run dev

Preparation

nilsroehrig/svelte-workshop-ijs-munich-2023

linkedin.com/in/nilsroehrig/

LinkedIn:

xing.com/profile/Nils_Roehrig2

Xing:

@drunknzombiecow

X:

Thank You!

Web-Apps with Svelte - A Practical Introduction (iJS Munich 2023)

By Nils Röhrig

Web-Apps with Svelte - A Practical Introduction (iJS Munich 2023)

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