Navigator.msLaunchUri() - Web APIs
successcallbackoptional a function matching the signature of mslaunchuricallback to be executed if the protocol handler is present.
... nohandlercallbackoptional a function matching mslaunchuricallback to be executed if the protocol handler is not present.
... see also mslaunchuricallback microsoft api extensions ...

Microsoft API extensions - Web APIs
eoframestepcompleted onmsvideooptimallayoutchanged msfirstpaint pinned sites apis mssitemodeevent mssitemodejumplistitemremoved msthumbnailclick other apis x-ms-aria-flowfrom x-ms-acceleratorkey x-ms-format-detection mscaching mscachingenabled mscapslockwarningoff event.msconverturl() mselementresize document.mselementsfromrect() msisstatichtml navigator.mslaunchuri() mslaunchuricallback element.msmatchesselector() msprotocols msputpropertyenabled mswriteprofilermark ...