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Lazy Loading iframes in SvelteKit: Ace Core Web Vitals # Lazy Loading iframes in SvelteKit: Ace Core Web Vitals #

Lazy Loading iframes in SvelteKit: Ace Core Web Vitals #

Updated 3 months ago

4 minute read

Gunning Fog Index: 5.5

Content by Rodney

🔥 Why Speed Matters #

Lazy loading iframes in SvelteKit does not have to give you a headache. If you have tried this kind of optimization 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.

📹 Lazy Loading iframes in SvelteKit: Video #

Please enable JavaScript to watch the video 📼

Loading iframes in SvelteKit

🖥 Code #

Package #

Install the vanilla-lazyload package.

shell

    pnpm add -D vanilla-lazyload

Lazy Loading iframes in SvelteKit Code #

src/routes/lazyload.svelte — 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       ></frame>
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       ></frame>
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       ></frame>
58     </div>
59     <!-- TRUNCATED... --> 
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 .

🗳 Poll #

How familiar are you with Core Web Vitals?

🔗 Lazy Loading iframes in SvelteKit: Links #

🙏🏽 SvelteKit Favicon: Feedback #

If you have found this video useful, see links below for further related content on this site. I do hope you learned one new thing from the video. Let me know if there are any ways I can improve on it. I hope you will use the code or starter in your own projects. Be sure to share your work on Twitter, giving me a mention, so I can see what you did. Finally, be sure to let me know ideas for other short videos you would like to see. Read on to find ways to get in touch, further below. If you have found this post useful, even though you can only afford even a tiny contribution, please consider supporting me through Buy me a Coffee.

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