do we have anything like isexists funcrion in suitescript?

Do a

search.lookupFields

. If it doesn't error it exists

no its for comparing two lists.

need more context, what are you checking for existence?

Exist where ? Array, object, or some record. you can just use array.indexof(whatever you want to check in the main array). One line of statement should tell you if it exist or not.