Override frappe call to intercept the call and act on basis of it.

FrappeCallIntercept.js

/**
 * Extends the functionality of Frappe's assignment feature for Leads.
 *
 * Problem:
 * When a document like a Lead is assigned to a user via the sidebar, the information about the assignment
 * (who it was assigned to, who assigned it, and when) is not stored in a way that can be easily displayed
 * on Kanban cards or list columns. It only results in a ToDo list item without these details on the Lead itself.
 *
 * Solution:
 * We are customizing frappe.call to intercept calls related to assignment actions. By overriding these calls,
 * we can capture necessary data and store it in custom fields on the Lead doctype. This allows displaying the
 * assignment information directly in the Lead's views (like Kanban or list views), enhancing visibility and
 * traceability.
 *
 * Strategy:
 * 1. Backup the original frappe.call to maintain standard functionality when needed.
 * 2. Override frappe.call to inject custom logic when assignment-related methods are invoked.
 * 3. Depending on the action (assign, unassign, close), update the Lead's custom fields to reflect these changes.
 */

frappe.ui.form.on('Lead', {
    setup: function(frm) {
        
        
        // Backup of the original frappe.call to use after custom logic
        const originalCall = frappe.call;
        
        // Override the standard frappe.call with customized behavior for assignment methods
        frappe.call = function(opts) {
            switch (opts.method) {
                case "frappe.desk.form.assign_to.add":
                    console.log("Assigned to:", opts.args.assign_to);
                    // Custom logic to add assignment info to a Lead-specific custom field
                    //frm.set_value('custom_assigned_to', opts.args.assign_to);
                    //frm.save();
                    break;
                case "frappe.desk.form.assign_to.remove":
                    console.log("Unassigned from:", opts.args.assign_to);
                    // Custom logic to clear or update the assignment info in Lead's custom field
                    //frm.set_value('custom_assigned_to', '');
                    //frm.save();
                    break;
                case "frappe.desk.form.assign_to.close":
                    console.log("Assignment closed for:", opts.args.assign_to);
                    // Additional logic to handle closing of assignments if necessary
                    break;
                default:
                    console.log("Operation not recognized", opts);
            }
            // Continue with the original frappe.call function to ensure normal operation
            return originalCall(opts);
        };
    }
});