var isvalid = 'marche pas';

function ValidField(validation, table, field, value) {
 
  var myRequest = new Request({url: 'index.php/webservice/validajaxfield', method: 'post', 
    onSuccess: function(responseText, responseXML) {
      SetIsValid(responseText)   
    }
  }).send('validation=' + validation + '&table=' + table + '&field=' + field + '&value=' + value);
  
  //alert(isvalid); 
}

function SetIsValid(value) {
  isvalid = value;  
}