title: Negative lookahead Regular Expression
body: <p>I want to match all strings ending in ".htm" unless it ends in "foo.htm".  I'm generally decent with regular expressions, but negative lookaheads have me stumped.  Why doesn't this work?</p>
  
  <pre><code>/(?!foo)\.htm$/i.test("/foo.htm");  // returns true. I want false.
  </code></pre>
  
  <p>What should I be using instead?  I think I need a "negative look<i>behind</i>" expression (if JavaScript supported such a thing, which I know it doesn't).</p>