title: matching filename base
body: <p>Still learning regex here but I need a little help.</p>
  
  <p>I have this string 
  <code>assets/BigBlueSomething_tn.jpg</code></p>
  
  <p>I need to match this
  <code>BigBlueSomething</code></p>
  
  <p>Closest I got is this
  <code>`[^\/][a-zA-Z]+_</code></p>
  
  <p>Problem is that I keep matching the underscore
  I've tried this <code>[^\/][a-zA-Z]+[^_]</code> at the advice from several other threads but to no avail. </p>
  
  <p>I'm writing in javascript, I believe there are some regex things that dont work in that language.</p>