some set polyfills

src/webpage/favorites.ts

@@ -38,7 +38,44 @@ type favandfreqimp = Omit<
 	| "heard_sound_frecency"
 	| "played_sound_frecency"
 >;
-
+Set.prototype.intersection ||= function <T>(set: Set<T>) {
+	const newSet = new Set();
+	for (const elm of this) {
+		if (set.has(elm)) {
+			newSet.add(elm);
+		}
+	}
+	return newSet;
+};
+Set.prototype.difference ||= function <T>(set: Set<T>) {
+	const newSet = new Set();
+	for (const elm of this) {
+		if (!set.has(elm)) {
+			newSet.add(elm);
+		}
+	}
+	return newSet;
+};
+Set.prototype.symmetricDifference ||= function <T>(set: Set<T>) {
+	const newSet = new Set();
+	for (const elm of this) {
+		if (!set.has(elm)) {
+			newSet.add(elm);
+		}
+	}
+	for (const elm of set) {
+		if (!this.has(elm)) {
+			newSet.add(elm);
+		}
+	}
+	return newSet;
+};
+Set.prototype.isDisjointFrom ||= function <T>(set: Set<T>) {
+	return this.symmetricDifference(set).size === 0;
+};
+Set.prototype.union ||= function <T>(set: Set<T>) {
+	return new Set([...this, ...set]);
+};
 export class Favorites {
 	owner: Localuser;
 	// ----- stuff that needs to store ----