> db_create_key(hDB, 0, "Equipment/Switching/Variables/DATA_WRITE", TID_INT);

you can also do this from javascript, too, using the db_create rpc call, see mjsonrpc_db_create() and 
example.html

> for (i = 0; i < lines.length; i++) {
>         modbset("/Equipment/Switching/Variables/DATA_WRITE[" + String(i) + "]", parseInt(lines[i]));
> }

this is wrong.

a) you are programming javascript as if it were C/C++. You think this code wrote lines.length() values 
to ODB, when what the code actually did is queued lines.length() RPC requests for later execution. 
Eventually some time later, each RPC request will open a connection to mhttpd, send a request, wait 
for mhtttpd to process it, etc. Where do you wait for the completion of all these RPCs before 
proceeding as if all the data has been successfully written to ODB? (answer: you cannot, javascript 
cannot "wait for things", instead you have to make chains of event handlers. javascript != C/C++. 
They are completely different).

b)  you should write the whole array in one operation instead of looping over each element. see 
mjsonrpc_db_paste() and example.html.

> After calling this function I have an array in the ODB now. For my understanding
> calling an INT like an array shouldn't be possible. So is this dangerous to do?

I do not understand your question about "calling an INT like an array". You are not calling anything 
called "INT". Your code has a loop, a call to parseInt() (defined where?) and a call modbset() 
(defined in mhttpd.js). It looks like correct javascript (it does not do what I think you expected it to 
do), what do you think is dangerous?

K.O.