Skip to main content


fires before a control or its checkbox is shown

beforeShow: (value: {[id: string]: boolean | string}, id?: string) => boolean | void;


  • value: object - the current value of the control. The object contains a set of key:value pairs where the key is the id of a checkbox and the value is the value/state of the checkbox.
  • id?: string - optional, the ID of a checkbox of the control


Return false to prevent a control or its checkbox from being shown; otherwise, true.


form.getItem("CheckboxGroup").events.on("beforeShow", function(value, id) {
console.log("beforeShow", value, id);
return true;

Related sample: Form. Hide/Show control

Change log:

The id parameter was added in v8.0