title: Javascript RegEx to return if string contains characters that are NOT in the RegEx
body: <p>I have a user created string. I am only allowing the characters <code>A-Z, a-z, 0-9, -,</code> and <code>_</code></p>
  
  <p>Using JavaScript, how can I test to see if the string contains characters that are NOT these? If the string contains characters that are not these, I want to alert the user that it is not allowed. </p>
  
  <p><strong>What Javascript methods and RegEx patterns can I use to match this?</strong></p>