Append hidden input to form

/** append an hidden input to a form */
function dynamicAddElementToForm( htmlForm, key, value )
{
    var obj = $("[name='"+ key +"']");
    if( obj.length ){
        obj.val(value);
    }else {
        var inputHiddenTemp = document.createElement('input');
        inputHiddenTemp.type = 'hidden';
        inputHiddenTemp.name = key;
        inputHiddenTemp.value = value;
        htmlForm.appendChild( inputHiddenTemp );
    }
}

/** use example */
var htmlForm = document.forms[IR_LocalNomeForm];
    dynamicAddElementToForm(htmlForm, "unParametroX", "true" );