Called when user changes a form field. This event is triggered each time user changes a form field. In the event object you can find previous and new value of the field. You can add event listener during the object creation: let form = new w2form({ name : 'form', url : 'server/post', record: { field_1 : 1, field_2 : 2 }, fields: [ { field: 'field_1', type: 'text', required: true }, { field: 'field_2', type: 'alphanumeric', required: true } ], onChange: function (event) { console.log(event); } }); or any time during run-time: w2ui.form.on('change', function (event) { console.log(event); }); The event handler is called before the default action of the event is triggered. You can cancel the default action by calling event.preventDefault(). To perform an action after the event is fully processed, define event.onComplete function. See events page in utilities for more details.