JS9 Demo: pan and zoom
Choose the View menu panner/magnifier for these images: Use the Web page panner/magnifier for these images: (Note that the panner has a separate toolbar while the magnifier overlays the toolbar on the display. This is an option for Web developers and can be ignored here ... unless you would like to tell us which you prefer!)
 
 

JS9 Demos:

web page configuration: multiple displays: plugins: colors: data analysis: FITS support: not often needed: