May 20th, 2020 × #svelte#webdev#javascript

Scott Teaches Wes Svelte and Sapper

In this episode Scott teaches Wes about Svelte, a new JavaScript framework that compiles away unused code for blazing fast performance. They cover features like built-in reactivity, cleaner templates vs JSX, routing with HTML anchors, and animations/transitions.


In this episode of Syntax, Scott teaches Wes about Svelte and Sapper — general premise, best practices, and more!

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Show Notes

03:14 - General premise

  • Sapper compiles away, removing framework code from build
  • Component & Props based
  • Easy reactivity
  • Built-in tools like animation
  • Template-based

07:57 - Svelte 101

  • .svelte files
  • Files can include <script>, <style>, and straight-up CSS
  • Variables are used in templates via {var} - <img {src} /> even works
  • Import component and use just like React and Vue

10:49 - Stylin'

  • All styles are scoped by default
  • global() to wrap around global declarations
  • Language type sass to use sass

12:22 - Reactivity

  • Baked in
    • let count = 0
    • count = count + 1 will reactively update in template
    • variables are essentially state
    • $: double = count + 2 - to create a reactive variable that updates when another variable updates
    • $: console.log(count) = will run whenever count is update a-la useEffect
    • $: if (count >10) = same... reactive if
    • <input bind:value={name} > updates let name in script

15:55 - Props

  • Same was React, but need to be exported before they can be used
  • Seems counterintuitive, but you get over it quickly
  • EZ defaults export let answer = 'a mystery';
import Nested from './Nested.svelte';

<Nested answer={42}/>
	export let answer = 'a mystery';

<p>The answer is {answer}</p>

20:08 - Template logic

  • If statements {#if user._id} {/if}

  • Loops {#each cats as kittens}

  • Promise tags

{#await promise}
{:then number}
	<p>The number is {number}</p>
{:catch error}
	<p style="color: red">{error.message}</p>

23:12 - Events

  • <button on:click={func} />
  • On directive
  • Functions can also be inline
  • Modifiers
<button on:click|preventDefault={handleClick}>
	Click me

26:11 - Baked-in goodies

  • Animation
  • Dimensions
<div bind:clientWidth={w} bind:clientHeight={h}><span style="font-size: {size}px">{text}</span></div>
  • Lifecycle methods
  • Advanced State Via Stores
    • A store is simply an object with a subscribe method that allows interested parties to be notified whenever the store value changes.
  • import { writable } from 'svelte/store';
  • export const count = writable(0);
  • count.update(0)
  • Slots
  • React helmet like stuff, ie svelte:head

36:39 - Sapper

  • Similar to Next.js
  • Folder routes
  • Static export with all of the good stuff like service workers and preloading


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