Microsoft Power Fx vs JavaScript: Which One Is Best for Your Dynamics 365 Forms

As a Senior Consultant working with Microsoft Dynamics 365 model-driven applications, I have learned over the years that form customization becomes a part of daily life for a developer. Whether it is showing or hiding fields, checking user input, or triggering conditional based logic, there are several ways to get the desired result needed. Traditionally, JavaScript has been the go-to tool for advanced customizations, but with Microsoft’s recent investments in Power Fx, there has been a shift into low-code form and field logic that can be managed without a deep development background. It has become a great way to simplify things and avoid writing complex JavaScript when it is not needed. In this post, I will break down the pros of both options and share some tips on when to use each in a Dynamics 365 form.  

To start, what is JavaScript? Well, it is a client-side scripting language used to customize Microsoft Dynamics 365 model-driven forms. Typically, developers use it to manipulate form elements like: 

• • Showing or hiding fields 

• • Enabling or disabling fields 

• • Interacting with field values 

• • Triggering conditional logic 

• • Calling external web APIs 

JavaScript is a great tool to learn and has many benefits, but what if you do not need complex code to achieve what you need on a Dynamics 365 form? The easier choice is to use formula columns using Microsoft Power Fx logic. Power Fx is a declarative Excel-like language used across the Power Platform. In model-driven apps, Microsoft has introduced it for things like: 

• • Command bar logic 

• • Field calculations 

• • Business rules 

• • Canvas app logic 

This makes it very accessible to functional consultants since it does not require web resources or JavaScript files and can be supported directly through the user interface. 

Most field data types are supported with Power Fx logic, which makes it very robust in what you can do with it. The fields supported are text, decimal, whole number, float number, yes/no, option sets, and datetime. The idea is that a “Formula” data type is selected when creating a new field, and then once your function is in place and working correctly, it will convert the field to the desired data type. For example: