Overview

1. The field may require updated options from external services in real-time. In such cases, the data can be fetched using the field lookup handler instead of overloading the menu click handler or form change handler.
2. The field may have more than 3000 options which is higher than the allowed limit. Therefore, instead of loading all the options in a single call, the developer can lookup/search the options in external services based on the query given by the user in real-time 

How to enable the field lookup handler?

When is the field lookup handler executed?

Implementation of field lookup handler

{
"lookup":false,
"options":[
{
"id":"4000000009065",
"label":"Zoho Payments"
},
{
"id":"4000000009079",
"label":"Zoho Projects"
}
]
}

The code given below is to display an information/blank state message when the handler could not fetch the results matching the user input:

{
      "info":"Please try again after some time."
}

Result:

The field lookup handler will not be executed in the following cases:

1. The field object's lookup value is set to be true, but the field lookup handler is not implemented.
2. The field lookup handler is implemented, but the field object's lookup value is set to be false.