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Lazy Loading iframes in SvelteKit: Ace Core Web Vitals

Loading iframes in SvelteKit

Lazy Loading iframes in SvelteKit: Ace Core Web Vitals

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πŸ”₯ Why Speed Matters

Lazy loading iframes in SvelteKit does not have to give you a headache. If you have tried this kind of optimisation on another framework, invested hours and only got marginal improvements, you should still read on. We use a lightweight package to add lazy loading so you don't end up with a bloated bundle. What's more we see you only need to make minimal changes to your code to implement lazy loading in SvelteKit. We implement the feature using a simple to use package and keep your SvelteKit sites on the right side of Google's new Core Web Vitals metrics.

Core Web Vitals are the metrics used by the Google algorithm to rank your site. Fall foul of the rules and risk seeing your ranking plummet! Not implementing features like lazy loading can negate all the gains from your SEO strategy.

Lazy loading is where the browser does not load all content on the page initially. As a user experience (UX) focussed developer you delay loading of large media, which is out of view, until it is about to come into view. We see in the video that this allows the page to load faster.

πŸ“Ή Lazy Loading iframes in SvelteKit: Video

Loading iframes in SvelteKit

πŸ–₯ Code

Package

pnpm i -D vanilla-lazyload
Install the vanilla-lazyload package.

Lazy Loading iframes in SvelteKit Code

src/routes/lazyload.svelte β€” click to expand code.
src/routes/lazyload.svelte
html
1<script>
2 import { browser } from '$app/env';
3 import lazyload from 'vanilla-lazyload';
4
5 let lazyloadInstance;
6 if (browser) {
7 lazyloadInstance = new lazyload();
8 }
9</script>
10
11<div class="container">
12 <div class="content">
13 <h1>Tokyo 2021 Highlights: Lazy Plugin</h1>
14
15 <h2>Day One</h2>
16 <div class="video-container">
17 <iframe
18 class="video-iframe"
19 loading="eager"
20 src="https://www.youtube-nocookie.com/embed/Hr_1VTJ6JLU"
21 title="Tokyo 2021 Highlights: Day One"
22 frameborder="0"
23 allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
24 allowfullscreen
25 />
26 </div>
27
28 <h2>Day Two</h2>
29 <div class="video-container">
30 <iframe
31 class="lazy video-iframe"
32 loading="lazy"
33 width="560"
34 height="315"
35 src=""
36 data-src="https://www.youtube-nocookie.com/embed/EQ8x3xy3-Ew"
37 title="Tokyo 2021 Highlights: Day Two"
38 frameborder="0"
39 allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
40 allowfullscreen
41 />
42 </div>
43
44 <h2>Day Three</h2>
45 <div class="video-container">
46 <iframe
47 class="lazy video-iframe"
48 loading="lazy"
49 width="560"
50 height="315"
51 src=""
52 data-src="https://www.youtube-nocookie.com/embed/Zd8T3Ng3DXI"
53 title="Tokyo 2021 Highlights: Day Three"
54 frameborder="0"
55 allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
56 allowfullscreen
57 />
58 </div>
59...
60 </div>
61</div>
62
63<style lang="scss">
64 .container {
65 display: flex;
66 flex-direction: column;
67 background-color: rgb(187, 25, 25);
68 color: #fff;
69 margin: 0;
70 padding: $spacing-4 0 $spacing-12;
71 }
72 .content {
73 display: flex;
74 flex-direction: column;
75 max-width: $max-width-container-md;
76 width: 100%;
77 margin: 0 auto;
78
79 h1 {
80 text-align: center;
81 }
82 }
83 .video-container {
84 position: relative;
85 overflow: hidden;
86 width: 100%;
87 margin: $spacing-4 auto;
88 padding-top: 56.25%; /* 16:9 aspect ratio */
89 }
90
91 .video-iframe {
92 position: absolute;
93 inset: 0;
94 width: 100%;
95 height: 100%;
96 }
97
98 @media (max-width: $max-width-container-md) {
99 .container {
100 padding: 0 $spacing-4;
101 }
102 }
103</style>
Responsive, lazy loading iframes in SvelteKit.

You can see the full code for lazy loading iframes in SvelteKit on the Rodney Lab Git Hub repo .

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