Backport Basilisk internal userscripts

browser/internaluserscripts/bundled-scripts/imagedecode-polyfill.user.js

@@ -0,0 +1,111 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// ==UserScript==
+// @name         HTMLImageElement.decode Polyfill (best-effort)
+// @namespace    internal-userscripts
+// @description  Adds a Promise-based decode() that resolves on load and rejects on error.
+// @match        *://*/*
+// @grant        none
+// @run-at       document-start
+// ==/UserScript==
+(function () {
+  "use strict";
+
+  var global = typeof window !== "undefined" ? window : null;
+  if (!global || !global.HTMLImageElement) {
+    return;
+  }
+
+  var proto = global.HTMLImageElement.prototype;
+  if (typeof proto.decode === "function") {
+    return;
+  }
+
+  var PromiseCtor = global.Promise;
+  if (typeof PromiseCtor !== "function") {
+    return;
+  }
+
+  function rejectPromise(error) {
+    return new PromiseCtor(function (resolve, reject) {
+      reject(error);
+    });
+  }
+
+  function hasLoadedImage(img) {
+    return img.complete && (img.naturalWidth > 0 || img.naturalHeight > 0);
+  }
+
+  function isBrokenImage(img) {
+    return img.complete && img.naturalWidth === 0 && img.naturalHeight === 0;
+  }
+
+  function decode() {
+    var img = this;
+    if (!(img instanceof global.HTMLImageElement)) {
+      return rejectPromise(new TypeError("decode can only be used on an HTMLImageElement"));
+    }
+
+    if (hasLoadedImage(img)) {
+      return PromiseCtor.resolve();
+    }
+    if (isBrokenImage(img)) {
+      return rejectPromise(new Error("Image decode failed"));
+    }
+
+    var src = "";
+    try {
+      src = img.currentSrc || img.src || "";
+    } catch (e) {}
+    if (!src) {
+      return rejectPromise(new Error("Image has no src"));
+    }
+
+    return new PromiseCtor(function (resolve, reject) {
+      var settled = false;
+
+      function cleanup() {
+        if (settled) {
+          return;
+        }
+        settled = true;
+        img.removeEventListener("load", onLoad, false);
+        img.removeEventListener("error", onError, false);
+      }
+
+      function onLoad() {
+        cleanup();
+        resolve();
+      }
+
+      function onError() {
+        cleanup();
+        reject(new Error("Image decode failed"));
+      }
+
+      img.addEventListener("load", onLoad, false);
+      img.addEventListener("error", onError, false);
+
+      if (hasLoadedImage(img)) {
+        cleanup();
+        resolve();
+      } else if (isBrokenImage(img)) {
+        cleanup();
+        reject(new Error("Image decode failed"));
+      }
+    });
+  }
+
+  try {
+    Object.defineProperty(proto, "decode", {
+      value: decode,
+      writable: true,
+      configurable: true
+    });
+  } catch (e) {
+    proto.decode = decode;
+  }
+
+  try { global.__internalUserscriptsImageDecodePolyfill = true; } catch (e) {}
+})();