Pineapple juice is very acidic! You'll need to open up the system ASAP to get to the spillage. Once you get it open following the IFIXIT Guides make sure you disconnect the battery first!
Now you'll need to get some distilled water (not tap!) using cotton swabs (Q-Tips) wash down the areas so you dilute and remove the acids within the juice. A second benefit here is distilled water will also help in removing the sugars as well. Once you have cleaned the area you'll need to use a high grade of Isopropyl alcohol (85% or better) to clean any oils and act as a drier to help in removing the last traces of distilled water. I would recommend letting the system dry in the warm sun light for a day (opened) before reassembly.
Follow this vid to pop the key caps to get underneath follow the same process as above. Just be careful on not snagging anything cleaning the key caps.