Stop the Save Event if Duplicate record is found

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Hi,

We have a requirement where During Record creation if  the current record's certain fields concatenated values are already present in some other record i.e if duplicate record is found, we have to cancel the save event and not save the record.

The above problem statement has to be achieved in Browser UI using javascript, 

After referring the documentation of BrowserUI Extensibility Framework: http://documentation.custhelp.com/euf/assets/devdocs/unversioned/BUI_Extensibility/topicrefs/EventHandler.html

We found that we can use parameter.getCurrentEvent.cancel() on WorkspaceRecord.addRecordSavingListener(), but we are getting an error as Uncaught (in promise) TypeError: parameter.getCurrentEvent.cancel is not a function