52 lines
1.6 KiB
TypeScript
52 lines
1.6 KiB
TypeScript
// Copyright: Ankitects Pty Ltd and contributors
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// License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
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function injectPreloadLink(href: string, as: string): void {
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const link = document.createElement("link");
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link.rel = "preload";
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link.href = href;
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link.as = as;
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document.head.appendChild(link);
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}
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export function allImagesLoaded(): Promise<void[]> {
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return Promise.all(
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Array.from(document.getElementsByTagName("img")).map(imageLoaded),
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);
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}
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function imageLoaded(img: HTMLImageElement): Promise<void> {
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return img.complete
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? Promise.resolve()
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: new Promise((resolve) => {
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img.addEventListener("load", () => resolve());
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img.addEventListener("error", () => resolve());
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});
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}
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function clearPreloadLinks(): void {
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document.head
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.querySelectorAll("link[rel='preload']")
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.forEach((link) => link.remove());
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}
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function extractImageSrcs(html: string): string[] {
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const tmpl = document.createElement("template");
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tmpl.innerHTML = html;
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const fragment = tmpl.content;
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const srcs = [...fragment.querySelectorAll("img[src]")].map(
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(img) => (img as HTMLImageElement).src,
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);
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return srcs;
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}
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export function preloadAnswerImages(qHtml: string, aHtml: string): void {
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clearPreloadLinks();
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const aSrcs = extractImageSrcs(aHtml);
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if (aSrcs.length) {
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const qSrcs = extractImageSrcs(qHtml);
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const diff = aSrcs.filter((src) => !qSrcs.includes(src));
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diff.forEach((src) => injectPreloadLink(src, "image"));
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}
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}
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