di-compiler VS reflect-metadata

DI-compiler

The custom di transformer replaces interfaces with according class instances. In the future, we will explicitly define which class should implement a particular interface.

Counter to this post, as soon as I read the title I knew what this was, & I knew it was speaking exactly to something we've wanted for a long time. This is asking for more official & better supported https://github.com/rbuckton/reflect-metadata .

TypeScript is a compiler. It has a lot of type information during compilation. We could write that type information out into a file. Instead what we do is throw that information out when the compile ends. Taking all that typing information & throwing it away at the end of compile time is a bad dumb & silly limitation. Especially for a language like JavaScript, which historically could be semi-proud it had such a strong Everything Is An Object philosophy running through it (such as the malleable prototype-based inheritance system); so much type information should be on that Class object. Reflect-metadata for example defined new methods on Reflect to store this metadata.

I could not be more delighted to see the pennon of this website go up. We needed a rallying point for this. We needed a rallying point for keeping class data around. A rallying point for enriching the runtime with good actionable data is a good rallying point.

It's not what's afoot here, but I think you're a bit off-base about the impossibility of adding even some type-safety. We might not be able to get exact TS type safety. But we can definitely build some safety in. Owing to the malleable prototype-based type system in JS, we can add getters/setters to objects to do a lot of type checking. This doesn't even begin to explore the possibility of what we might do with es2015's proxies, which could allow even more interesting checks to be layered in. I also wish JS had an official AST (and renderer), so had more official options for code-rewriting that might let us weave in type checks.

What we can do as programmers is limited by what we have at our disposal. Not throwing out all the typing information, keeping it around at runtime, opens a lot of interesting doors.

Second, TypeScript 5.0 cannot emit decorator metadata. Subsequently, it doesn’t integrate with the Reflect API and won’t work with the reflect-metadata npm package.

Database columns will be mapped to domain object properties using decorators. This will include relationships and enum types. reflect-metadata stores metadata about the classes and properties. Most of the work is a simple map for each class, renaming db column properties to domain model properties and vice versa. Reflect.defineProperty holds a list of field metadata on the target class. This is where more database ORM logic could live in the future such as column type, length, etc. A base domain model entity will use this metadata to map the models appropriately.