How to change the label of a widget

/**  
  widget_id: element itself, not string
  widget_label: as a string
*/

function setWidgetLabel(widget_id, widget_label) {
    try {
       widget_id.setLabel(widget_label);
    } catch (err) {}
}

Examples

setWidgetLabel(id_widget_1, "Save");
setWidgetLabel(id_widget_2, "Submit");