musical transposition in javascript

I'm trying to make a transposer in JavaScript..
Give it a key and a scale/mode and it will generate it for you
For instance
C Lydian (WWWHWWH) is C D E F# G A B
C Aeolian (WHWWHWW) is C D Eb F G Ab Bb
I cannot for the life of me figure out how to accomplish this.
Thoughts?
>inb4 SICP

>>4 I thought about that, but then what do for flats and sharps?
In music theory, you can't use sharps and flats in the same key, you must use one or the other
Also, that doesn't help me generate modes that would only change the key