How to set a focus to an input field in method invoked after onchange() event

<spring:message code="template.fields.label.from"/>:
       <mvc:input  path="templateFields.selectorRangeFrom"
       onchange="validateNumber('templateFields.selectorRangeFrom',true)"/>
   <spring:message code="template.fields.label.to"/>:
      <mvc:input path="templateFields.selectorRangeTo"
     onchange="validateNumber('templateFields.selectorRangeTo',true)"/>

function validateNumber(index,isInteger) {
 var object = document.getElementById(index);
 var value = object.value;
 if (testNumeric2(value,isInteger)==false)       {
         alert('Please correct the value: ' + value);
         object.focus();
         object.select();
         return false;
 }
return true;
 }

if (! /** check field **/) {
   /** show error **/
   setTimeout((function() { object.focus() }), 0);
}