move TransformEvent to own file

src/common/TransformEvent.ts

@@ -0,0 +1,61 @@
+import type { TransformDOMRectReadonly } from './TransformDOMRect';
+
+// TODO: expose previous and current rects
+export class TransformEvent extends Event {
+  readonly #current: TransformDOMRectReadonly;
+  readonly #previous: TransformDOMRectReadonly;
+
+  constructor(current: TransformDOMRectReadonly, previous?: TransformDOMRectReadonly) {
+    super('transform', { cancelable: true, bubbles: true });
+    this.#current = current;
+    this.#previous = previous ?? current;
+  }
+
+  get current() {
+    return this.#current;
+  }
+
+  get previous() {
+    return this.#previous;
+  }
+
+  #xPrevented = false;
+  get xPrevented() {
+    return this.defaultPrevented || this.#xPrevented;
+  }
+  preventX() {
+    this.#xPrevented = true;
+  }
+
+  #yPrevented = false;
+  get yPrevented() {
+    return this.defaultPrevented || this.#yPrevented;
+  }
+  preventY() {
+    this.#yPrevented = true;
+  }
+
+  #heightPrevented = false;
+  get heightPrevented() {
+    return this.defaultPrevented || this.#heightPrevented;
+  }
+  preventHeight() {
+    this.#heightPrevented = true;
+  }
+
+  #widthPrevented = false;
+  get widthPrevented() {
+    return this.defaultPrevented || this.#widthPrevented;
+  }
+  preventWidth() {
+    this.#widthPrevented = true;
+  }
+
+  #rotatePrevented = false;
+  get rotatePrevented() {
+    return this.defaultPrevented || this.#rotatePrevented;
+  }
+  preventRotate() {
+    this.#rotatePrevented = true;
+  }
+}