title: Regular expression in Javascript to validate US phone number
body: <p>I'm using <code>/^\d{3}\ ?-? ?\d{3}\ ?-? ?\d{4}$/;</code> to validate US phone numbers. Can anyone tell me how to modify this expression to make <code>()</code> optional on the first set of numbers.</p>
  
  <p>For example: it should work for <code>(123)234-2345</code> , <code>123-345-4567</code> , <code>123 - 345 - 4567</code> , <code>123345-6789</code></p>