Como essa pergunta foi mostrada no stackoverflow em 2019, gostaria de adicionar minha contribuição usando um JavaScript mais moderno.
Especificamente, para folhas de estilo CSS que não são embutidas - uma vez que já foi abordado na questão original, de alguma forma.
Em primeiro lugar, observe que ainda não temos objetos de folha de estilo construtíveis. No entanto, esperamos que eles sejam desembarcados em breve.
Nesse ínterim, presumindo o seguinte conteúdo HTML:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<link id="theme" rel="stylesheet" type="text/css" href="./index.css" />
<script src="./index.js"></script>
</head>
<body>
<p>Hello World</p>
<button onclick="reload('theme')">Reload</button>
</body>
</html>
Poderíamos ter, em index.js:
// Utility function to generate a promise that is
// resolved when the `target` resource is loaded,
// and rejected if it fails to load.
//
const load = target =>
new Promise((rs, rj) => {
target.addEventListener("load", rs, { once: true });
target.addEventListener(
"error",
rj.bind(null, `Can't load ${target.href}`),
{ once: true }
);
});
// Here the reload function called by the button.
// It takes an `id` of the stylesheet that needs to be reloaded
async function reload(id) {
const link = document.getElementById(id);
if (!link || !link.href) {
throw new Error(`Can't reload '${id}', element or href attribute missing.`);
}
// Here the relevant part.
// We're fetching the stylesheet from the server, specifying `reload`
// as cache setting, since that is our intention.
// With `reload`, the browser fetches the resource *without* first looking
// in the cache, but then will update the cache with the downloaded resource.
// So any other pages that request the same file and hit the cache first,
// will use the updated version instead of the old ones.
let response = await fetch(link.href, { cache: "reload" });
// Once we fetched the stylesheet and replaced in the cache,
// We want also to replace it in the document, so we're
// creating a URL from the response's blob:
let url = await URL.createObjectURL(await response.blob());
// Then, we create another `<link>` element to display the updated style,
// linked to the original one; but only if we didn't create previously:
let updated = document.querySelector(`[data-link-id=${id}]`);
if (!updated) {
updated = document.createElement("link");
updated.rel = "stylesheet";
updated.type = "text/css";
updated.dataset.linkId = id;
link.parentElement.insertBefore(updated, link);
// At this point we disable the original stylesheet,
// so it won't be applied to the document anymore.
link.disabled = true;
}
// We set the new <link> href...
updated.href = url;
// ...Waiting that is loaded...
await load(updated);
// ...and finally tell to the browser that we don't need
// the blob's URL anymore, so it can be released.
URL.revokeObjectURL(url);
}
