Problem with storage write to pos 0

At least in my test, it did not matter, writing data or an empty string.
writing undefined or nothing gives an error, but, surprise,surprise, a file is created.
@fanoush, Data cannot be overwritten, thats a good point. I did not read this before.
BTW, try this:

st.write("a","",0,10);
=true
>st.read("a");
="\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"
>st.readArrayBuffer("a");
=new Uint8Array([255, 255, 255, 255, 255, 255, 255, 255, 255, 255]).buffer
>st.write("a","AB",0);
=true
>st.read("a")
="AB"
>st.readArrayBuffer("a");
=new Uint8Array([65, 66]).buffer
>st.write("a","CD",2);
Uncaught Error: Too much data for file size
 at line 1 col 20
st.write("a","CD",2);
                   ^
>st.write("a",[66,67],2);
Uncaught Error: Too much data for file size
 at line 1 col 23
st.write("a",[66,67],2);
                      ^
>st.read("a");
="AB"
> 

On the other hand, this works

>st.write("a","abcd",0,10);
=true
>st.readArrayBuffer("a");
=new Uint8Array([97, 98, 99, 100, 255, 255, 255, 255, 255, 255]).buffer
>st.write("a","efg",4);
=true
>st.readArrayBuffer("a");
=new Uint8Array([97, 98, 99, 100, 101, 102, 103, 255, 255, 255]).buffer
>st.read("a")
="abcdefg\xFF\xFF\xFF"
> 

Anyway, it works for me now ;-)