title: regular expression string replacement
body: <p>I have a url like this:</p>
  
  <pre><code> http://mywebsite.com/my-very-long-product-title/my_sku,default,pd.html
  </code></pre>
  
  <p>I want to replace this string with</p>
  
  <pre><code>http://mywebsite.com/-/my_sku,default,pd.html
  </code></pre>
  
  <p>I'm using javascript only.  The rule is I want to always replace everything between the single slashes closest to the end of the string.</p>