I am not really sure I completely understood what you are after 🙂
Are you referring to creating a custom node code which has a string value input?
If so, this can be done in many ways, but the easiest one is creating what is called a SimplexNode [DOCS LINK].
here is a very simple example of a node with a string ValueInput and a string ValueOutput (as well as Flow Input and Out):
//do something with the input value, return something
returnvalue;
}
}
Is that close to what you are after?
Please refer to the docs link above for a reference to the various SimplexNode types you can derive from and how to use them, but if you still have any questions at all, please let me know.