implemented new fitView logic

packages/react/src/hooks/useOnViewportChange.ts

@@ -4,18 +4,35 @@ import type { OnViewportChange } from '@xyflow/system';
 import { useStoreApi } from './useStore';
 
 export type UseOnViewportChangeOptions = {
+  /** Gets called when the viewport starts changing. */
   onStart?: OnViewportChange;
+  /** Gets called when the viewport changes. */
   onChange?: OnViewportChange;
+  /** Gets called when the viewport stops changing. */
   onEnd?: OnViewportChange;
 };
 
 /**
- * Hook for registering an onViewportChange handler.
+ * The `useOnViewportChange` hook lets you listen for changes to the viewport such
+ * as panning and zooming. You can provide a callback for each phase of a viewport
+ * change: `onStart`, `onChange`, and `onEnd`.
  *
  * @public
- * @param params.onStart - gets called when the viewport starts changing
- * @param params.onChange - gets called when the viewport changes
- * @param params.onEnd - gets called when the viewport stops changing
+ * @example
+ * ```jsx
+ *import { useCallback } from 'react';
+ *import { useOnViewportChange } from '@xyflow/react';
+ *
+ *function ViewportChangeLogger() {
+ *  useOnViewportChange({
+ *    onStart: (viewport: Viewport) => console.log('start', viewport),
+ *    onChange: (viewport: Viewport) => console.log('change', viewport),
+ *    onEnd: (viewport: Viewport) => console.log('end', viewport),
+ *  });
+ *
+ *  return null;
+ *}
+ *```
  */
 export function useOnViewportChange({ onStart, onChange, onEnd }: UseOnViewportChangeOptions) {
   const store = useStoreApi();