trackElement method added

package.json

@@ -30,5 +30,10 @@
     "typedoc": "^0.11.1",
     "typescript": "^2.9.2",
     "update-json": "^1.0.0"
+  },
+  "dependencies": {
+    "@gen-tech/js-utils": "^0.16.1",
+    "@gen-tech/resize-manager": "^0.1.4",
+    "@gen-tech/scroll-manager": "^0.2.1"
   }
 }

src/index.ts

@@ -1 +1,5 @@
-export { PositionTracker } from "./position-tracker";
+import { PositionTracker } from './position-tracker';
+
+export { PositionTracker } from "./position-tracker";
+
+export default new PositionTracker();

src/position-tracker.ts

@@ -1 +1,45 @@
-export class PositionTracker {}
+import scrollManager from "@gen-tech/scroll-manager";
+import resizeManager from "@gen-tech/resize-manager";
+import { Observable } from 'rxjs';
+import { merge, map, throttleTime } from "rxjs/operators";
+import { noop } from "@gen-tech/js-utils";
+
+export interface IElementPosition {
+  left: number;
+  top: number;
+}
+
+export class PositionTracker {
+
+  constructor(
+    private defaultThrottleTime = 90
+  ) {
+  }
+
+  public trackElement(element: HTMLElement): Observable<IElementPosition> {
+    const trigger = resizeManager.root.throttleBy(0)
+      .pipe(
+        merge(scrollManager.root.throttleBy(0)),
+        merge(resizeManager.observe(element.parentElement).throttleBy(0)),
+        merge(scrollManager.observe(element.parentElement).throttleBy(0))
+      );
+
+    return this.trackElementByOwnTrigger(element, trigger);
+  }
+
+  public trackElementByOwnTrigger(
+    element: HTMLElement,
+    trigger: Observable<any>,
+    _throttleTime = this.defaultThrottleTime
+  ): Observable<IElementPosition> {
+    return trigger.pipe(
+      throttleTime(_throttleTime),
+      map(() => this.getElementPosition(element))
+    );
+  }
+
+  public getElementPosition(element: HTMLElement): IElementPosition {
+    const { top, left } = element.getBoundingClientRect();
+    return {top, left};
+  }
+}