I think your program should follow the following basic steps:
Input >> Interpret >> Validate >> Solve >> Translate >> Output
Input: Accept text from user (or
test case)
Interpret : Convert number into text form. e.g. π to "10"
Validate : Ensure the equations are valid, e.g. 10 xx 10, 10 ++ 10 -- 3, etc...
Solve : This is where you can get creative, you can either make a full fledged number parser or you can simply use the underlying javascript engine or some other library to get the final numerical answer
Translate : convert final result back to emoji like "100" to π―and so on... You can even randomly choose to either output a number or emoji for every number
Output : Show the result to the user
We would love to see what you've made so far !