title: Check if string contains any letter (Javascript/jquery)
body: <p>How can i check if a string contains any letter in javascript?</p>
  
  <p>Im currently using this to check if string contains any numbers:</p>
  
  <pre><code>    jQuery(function($){
      $('body').on('blur change', '#billing_first_name', function(){
      var wrapper = $(this).closest('.form-row');
      // you do not have to removeClass() because Woo do it in checkout.js
      if( /\d/.test( $(this).val() ) ) { // check if contains numbers
      wrapper.addClass('woocommerce-invalid'); // error
      } else {
      wrapper.addClass('woocommerce-validated'); // success
      }
      });
      });
  </code></pre>
  
  <p>However i want it to see if it contains any letters.</p>