In simple web parts like this, we should keep the JavaScript payload low. This means that, when you are building a web part with a few fields and simple communication needs, we don't need Angular or React or even jQuery, as you can see. However, as business requirements for the user experience grow, the need for third-party frameworks and libraries increases. The subject is covered in detail in Chapter 9, Using React and Office UI Fabric React Components, and Chapter 10, Working with Different JavaScript Frameworks and 3rd Party Frameworks.
Simple requirements can be addressed with simple solutions. For example, if we want to change the behavior of our web part so that it doesn't allow clicking of the Send button when there is no text in the text field, we can make the following changes.
In the render function, just before the function ends, add the following line:
button.disabled = true;
Then, replace the setComment function with the following:
private...