title: Evaluate conditionals at compile time in babel / webpack
body: <p>I have a config file where I have a variable that can have the value X or Y depending if it's prod or dev.</p>
  
  <p>I want to evaluate it at compile time. </p>
  
  <p>I was able to get the NODE_ENV value from babel-plugin-transform-node-env-inline but can't figure out how to evaluate the expression. I tried babel-plugin-transform-conditionals but it throws strange code errors. Errors that don't exist.</p>
  
  <p>I can evaluate at runtime since in that case both prod and dev values will be available in app.js, which I can't have.</p>
  
  <p>No idea where to go from here!!</p>
  
  <p>Any totally different solution would work too (like somehow compile a different file), but not sure how to go about it.</p>