Hi,
Do you mean in an adaptive form?
If so you can do something like the following:
window.addEventListener("bridgeInitializeStart", function (evnt) {
// get hold of the guideBridge object
var gb = evnt.detail.guideBridge;
//wait for the completion of adaptive forms
gb.connect(function () {
//this function will be called after adaptive form is initialized
gb.on("elementFocusChanged", function (event, data) {
// validate field
});
});
});