I want to use the returned value of the inside function as the new parameter for the outer function.

This is what I had in mind. I wanted to see if i can manipulate values without declaring a variable.

Object.keys(data).map( ( item = (item) => data[item]) , index) => (
   <>
      something in here
   </>
));

Inside function here is (items)=> data[item] which returns a new value for parameter as data[item] and outer function is the function inside map ie

( item = (item) => data[item]) , index) => (
   <>
      something in here
   </>
)