Page preloader for Sapper

I believe this component should be included into sapper-template by default as due to it's AJAX nature page loading looks a bit broken now.

Try to enable "Slow 3G" throttling in Chrome DevTools and follow a link on a sapper-based site. Choose a link without prefetch attribute to see the strongest effect. Did it felt broken enough that you've clicked the link twice or tried another one? :)

To see what exactly went wrong you can disable js and try to follow the same link again. You'll see:

• toolbar reloading icon turns into a cross
• tab favicon turns into a spinner
• page url will change only after the page loading

Nothing of these happens with enabled js, but instant url change is probably the most noticeable effect.

A usual way of fixing this is adding some kind of loading indicator. And here's how to add a top bar - probably the most common type of these indicators natively existing in mobile browsers.

Setup

Install the component:

npm i sapper-page-loading-bar

and include it at the top of your src/routes/_layout.svelte, you can also add a transition effect on page loading:

<PageLoadingBar {preloading}/>

{#if !$preloading}
    <main transition:fade>
        <slot></slot>
    </main>
{/if}

<script>
    import { fade } from "svelte/transition"
    import { stores } from "@sapper/app"
    import PageLoadingBar from "sapper-page-loading-bar/PageLoadingBar.svelte"

    const { preloading } = stores()
</script>

Tuning

While preloading parameter is required, there's also a few optional of them you can use to shape the preloader appearance:

• height - height of the preloader line
• color1 and color2 - its colors