Eyas's Blog

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Learning by Implementing: Observables

Sometimes, the best way to learn a new concept is to try to implement it. With my journey with reactive programming, my attempts at implementing Observables were key to to my ability to intuit how to best use them. In this post, we'll be trying various strategies of implementing an Observable and see if we can make get to working solution.

I'll be using TypeScript and working to implement something similar to RxJS in these examples, but the intuition should be broadly applicable.

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Schema.org Classes in TypeScript: Properties and Special Cases

JSON-LD Logo in Public Domain.

In our quest to model Schema.org classes in TypeScript, we've so far managed to model the type hierarchy, scalarDataTypevalues, and enums. The big piece that remains, however, is representing what's actually inside of the class: it's properties.

After all, what it means for a JSON-LD literal to have "@type" equal to "Person" is that certain properties — e.g. "birthPlace" or "birthDate", among others — can be expected to be present on the literal. More than their potential presence, Schema.org defines a meaning for these properties, and the range of types their values could hold.

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Schema.org DataType in TypeScript: Structural Typing Doesn't Cut It

JSON-LD Logo in Public Domain.

Schema.org has a concept of a DataType, things like Text, Number, Date, etc. In JSON-LD, we represent these as strings or numbers, rather than array or object literals. This data could describe the name of a Person, a check-in date and time for a LodgingReservation, a URL of a Corporation, publication date of an Article, etc. As we'll see, the Schema.org DataType hierarchy is far richer than TypeScript's type system can accommodate. In this article, we'll go over the DataType hierarchy and explore how much type checking we can provide.


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Schema.org Enumerations in TypeScript

JSON-LD Logo in Public Domain.

Last time, we talked about modeling the Schema.org class hierarchy in TypeScript. We ended up with an elegant, recursive solution that treats any type Thing as a "@type"-discriminated union of ThingLeaf and all the direct sub-classes of the type. The next challenge in the journey of building TypeScript typings for the Schema.org vocabulary is modeling Enumerations.

Let's look at a few examples from the Schema.org website to get a better sense of what Enumerations look like.

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