Compare new date with Existing date

Hi Experts,

I have one custom entity and in that I have two fields that "Valid from" and "Valid to".These two are indicates that a work starts from and finish in between these two dates.

Now my requirement is if I have a training record from 21st Jan to 30th Jan.

And Then If I am trying to create any record between these days like 24th to 27th Jan then CRM should give an error message that we already have a training on these dates. For this I already generate one FetchXML file and after that I stucked.Now what should I do to solve this issue using Javascript?

Thanks in advance for help.