Fixing "404 Page not found" on New/Edit/Display Forms and List Views After Custom Web Template Site Migration (2010 -> 2013)

SharePoint migration is always a challenge. And the more customizations you have the more challenging it is.
In this post I want to describe the solution to fix "404 Page not found" issue that may occur after migrating sites based on custom web templates and custom features.


SharePoint Framework Extensions: React Slider Field Customizer

In this post I want to show you step-by-step implementation of SharePoint Framework Field Customizer - React Slider Customizer.
UPDATE: on 9/25/2017 SPFx Extensions were GA-ed. The post is updated to contain the latest version of API.
Key features of the sample: For those who doesn't want to read the post but need the code - you can get it from here.