String.prototype.trim = function() 
{
  return( this.replace(/^\s*([\s\S]*\S+)\s*$|^\s*$/,'$1') ); 
}

function sForm(frm){
  if((document.forms[frm].city.value).trim()==""){
    alert('Please enter a Destination City');
    document.forms[frm].city.value="";
    document.forms[frm].city.focus();
  }
  else{
    document.forms[frm].submit();
  }
}