On August 20th, the team behind TypeScript officially released its 4.0 version. This is the most advanced version of the language, interpreter, and even their website to this date.

And with the announcement came the list of updates, which surprisingly for a major version change, they weren’t that many. Don’t get me wrong, they’re major changes that required a lot of design work and a lot of coding hours by a lot of people. And in this article I’m going to cover the major ones, if you want to read the official release with everything that changed, you can click here.

So without further ado, let’s get to the list of the changes I’m most excited about, shall we?

Class Property Inference from Constructors

Number one of the list is this little puppy. Every time the language (or the interpreter) works in your favor in order to save you time and keystrokes, I’m up for it. In this case, TypeScript is now performing control flow analysis to understand what kind of values you’re assigning to your class’ properties. If the analysis is able to determine that there are no unreachable paths, then it’ll be able to assume their types.

The second version of the class has one code path (the IF statement) that is not always going to be used, which means that first_name and last_name won’t always have a value assigned with this code. And because of that TS’s interpreter won’t be able to infer the type for them. The first example though, with clear code paths, is a perfect sample of how you can avoid having to define the types and let the interpreter infer them from your logic.

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