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Prevent FOUT by injecting new CSS first #146

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Merged
arrowtype merged 1 commit into from
Oct 3, 2025
Merged

Prevent FOUT by injecting new CSS first #146

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25 changes: 16 additions & 9 deletions src/service-worker.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,23 +10,30 @@ let injectedCSS = {};
* @param {string} text
*/
async function insertOrReplaceCss(tabId, category, text) {
if (tabId in injectedCSS && category in injectedCSS[tabId]) {
if (injectedCSS[tabId][category] == text) {
return;
}
const previousCss = injectedCSS[tabId]?.[category];
if (previousCss == text) {
return;
}

// Insert new CSS...
await chrome.scripting.insertCSS({
target: { tabId },
css: text
});

if (previousCss) {
// ...and remove old CSS *afterwards* to prevent FOUT
await chrome.scripting.removeCSS({
target: { tabId },
css: injectedCSS[tabId][category]
css: previousCss
});
}

if (!(tabId in injectedCSS)) {
injectedCSS[tabId] = {};
}

injectedCSS[tabId][category] = text;
await chrome.scripting.insertCSS({
target: { tabId },
css: text
});
}

// Do the thing! (Generate stylesheet and inject into active tab)
Expand Down