Line number mismatch

I'm debugging the client-side JS of an isomorphic node.JS application. The JS served to the browser (Chrome) has 2 lines are the top which are not in the original source:

(function(require,module,exports,__dirname,__filename,process,global
/**/) {

Because of this, debugging against the original source is difficult (if not impossible), because the line numbers in the displayed source in WebStorm don't match the line numbers of the executed source in the client. Thus, I end up debugging "empty" lines of code (for example).

Can someone suggest how to deal with this? 

Thank you

Gary