# \[javascript\] vtkRenderWindowInteractor doesn't have the function addObserver
**URL:** https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624
**Category:** Support
**Created:** [June 7, 2023, 10:19am UTC](https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624 "2023-06-07T10:19:40Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Alex\_Vergara](https://discourse.vtk.org/u/Alex_Vergara)
#### Post date: [June 7, 2023, 10:19am UTC](https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624/1 "2023-06-07T10:19:40Z")
I want to associate a mousemove event handler to an interactor. this is done in python as
```auto
renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.AddObserver("MouseMoveEvent", mousemove)
```
The problem is that this function doesn’t exist in vtk.js. Is there any way to achieve this?
I am currently using the container of the interactor `container.addEventListener('mousemove', mousemove);`. But this creates some conflict with current mousemove events (when some manipulator is activated).
Is there a right way of doing this?
My mousemove function is
```auto
performanceTimer=performance.now();
function mousemove(event){
// If any interactor is active or mouse moves too fast do nothing
if ((performance.now()-performanceTimer<10) || interactor.getInteractorStyle().currentManipulator){
return;
} else {
// Do stuff
performanceTimer=performance.now();
}
}
```
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [June 7, 2023, 3:38pm UTC](https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624/2 "2023-06-07T15:38:43Z")
vtkRenderWindowInterator trigger [the following set of events](https://github.com/Kitware/vtk-js/blob/master/Sources/Rendering/Core/RenderWindowInteractor/index.js#L28-L66).
So you should be able to do the following
```js
const subscription = renderWindowInteractor.onMouseMove(mousemove);
```
---
### Author:  [@Alex\_Vergara](https://discourse.vtk.org/u/Alex_Vergara)
#### Post date: [June 8, 2023, 8:49pm UTC](https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624/3 "2023-06-08T20:49:27Z")
Hello and thanks
Main question:
Does this onMouseMove come with a throttler, or do I have to make my own hack?
The main problem I have now is that my throttler messes up with the interactor event and the interaction happens only every number of ms (if I decrease them then the system halts with many calls to mousemove, if I increase it all the interactors became laggy)
I need to display the scalar contained int the cell under the mouse, but if any interactor is activated, then don’t trigger this mouse move function.
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [June 8, 2023, 10:11pm UTC](https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624/4 "2023-06-08T22:11:30Z")
You can [throttle](https://github.com/Kitware/vtk-js/blob/master/Sources/macros.js#L1131-L1154) the mousemove callback by decorating it.
---
### Author:  [@Alex\_Vergara](https://discourse.vtk.org/u/Alex_Vergara)
#### Post date: [June 9, 2023, 11:37am UTC](https://discourse.vtk.org/t/javascript-vtkrenderwindowinteractor-doesnt-have-the-function-addobserver/11624/5 "2023-06-09T11:37:36Z")
I have solved the interaction conflict by changing this `interactor.getInteractorStyle().currentManipulator` into `event.button>=0`. Everything is working as intended now.
Somehow the current manipulator way is not working