`async` - when `true`, the paper uses asynchronous rendering to display graph cells (i.e. cells added either with `graph.resetCells()` or `graph.addCells()` methods).

This is very useful for adding a large number of cells into the graph. The rendering performance boost is significant and it doesn't block the UI. However, asynchronous rendering brings about some caveats – at the time when you call another function...

- ...the views of freshly added cell models may not have yet been added to this paper's DOM.
- ...some views may have been removed from the DOM by the `paper.options.viewport` function.
- ...views already present in the DOM may not have been updated to reflect changes made in this paper's graph since the last render.
- ...re-rendering may have been manually disabled with `paper.options.frozen` or `paper.freeze()`.

This is an issue because certain CellView/Paper methods require the view to be updated and present in the DOM to function properly (e.g. `paper.findViewByModel()` or `element.findView()`/`link.findView()`, as well as `paper.getContentBBox()` and `elementView.getBBox()`/`linkView.getBBox()`).

The problem may be circumvented in several Paper methods via the `useModelGeometry` option to force using model calculations instead of view measurements (e.g. `paper.getContentBBox()`, `paper.getContentArea()`, `paper.scaleToFit()`, `paper.fitToContent()`). In this case, the methods refer to the (always up-to-date) model data.

For the methods that truly need a to refer to a CellView, one way to prevent inconsistencies is to rely on the `'render:done'` paper event. This event signals that all scheduled updates are done and that the state of cell views is consistent with the state of the cell models.

Alternatively, you may trigger a manual update immediately before a sensitive function call. JointJS offers several suitable methods:

- `paper.requireView()` - bring a single view into the DOM and update it.
- `paper.dumpViews()` - bring all views into the DOM and update them.
- `paper.updateViews()` - update all views.