Ask HN: How to inject code within a js so that it cannot be auto detected

I have a piece of code (a) which i would like to inject in an existing piece of code (b). I would not like this injection to be auto detected. It is assumed that (b) is always subject to change

My approach was to create a random var (x) which would have the code (a) split and concatenated in random locations within (b)

For example:

Var x="var code=fu";{random piece of (b)};x+="nction(";{random piece of (b)};x+="){}";{random piece of (b)};eval(x);{random piece of (b)}

1. Would you approach this problem differently? 2. How would you detect for root-level code within (b) - aka random locations outside loops or functions