Client script syntax question

Client script syntax question

This script run in a Canvas onBeforeUpdate event.

What's incorrect about this syntax?

/** 
 * log("sample logging statement") --> can be used to print any data in the browser console.
 * ZDK module can be used for customising the UI and other functionalities.
 * return false to prevent <SAVE> action
**/

var deal = ZDK.Apps.CRM.Deals.fetchById("4356038000026643023");
var street_1 = zdk.apps.crm.Ship_Street_1 = "123 Main Street";
var response = deal.__update;

I also tried resposne = deal.update()l