Regular expression allowing only characters that will not break a link

Anybody can help me with regular expression which will only accept alphabetical letters from English alphabet and numbers without whitespaces ( ÖÜÕÖ and similar characters + whitespaces will break the HTML link this thing is creating )? I currently have : /[A-Za-z ]\S+$/ but this will allow whitespaces and ÖÜÄ and similar at the beggining.

function validatenumber(el) {
   var regex = /[A-Za-z ]\S+$/;    
   if( !regex.test(el.value) ) {
      alert('invalid value');
  }else{
          alert('correct value'); 
  }
}

http://ift.tt/1UeAVyt Here's a fiddle.