beforeShow

fires before a control is shown

beforeShow: (value: undefined) => boolean | void;

Parameters:

• value: undefined - the current value of the control, null

Returns:

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

Example

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