Calculator - React typescript

My focus with this project was to practice typescript. One of the main struggles when starting something includes the limitation of how, why and when to use some of the (types) in this case. There are 2 bugs that I still have to fix:

1. To replicate the first bug, start by typing a decimal point - what i wanted is have a 0. printed on the screen. Instead what i get is a zero and the decimal point will only show when another number which is not zero is entered . Eg if i type 0.003 - the first 0.00 is not shown upon typing - zero will continue to be displayed until the 3 is typed.
2. The second bug is identical to the first in that it also involves a fraction. If a am to type 2.005008 - a full display of numbers will be shown when 5 and then 8 is entered. in between it will be 2 then 2.005 when 5 is typed and lastly the full number when 8 is typed.

If there are any more bugs , please let me know as well as improvements that should be carried out.