Statically Typed Data Validation with JSON Schema and TypeScript

One super common problem on TypeScript projects is figuring out how to validate data from external sources and tie that validated data to TypeScript types. In these situations, you generally have a few options:

  1. Define types and validations separately, and type them together with Type Guards.
  2. Use an internal DSL such as io-ts to build both a validator and the TypeScript type at the same time.
  3. Use an external DSL such as JSON Schema to define the validator, and derive the TypeScript type from there.

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Flavoring: Flexible Nominal Typing for TypeScript

Recently, we’ve been making heavy use of TypeScript at Atomic Object. We love the great tooling and instant feedback we get with the language’s powerful type system. TypeScript’s structural type system gives us a lot of powerful tools for making invalid states unrepresentable, thereby pointing out bugs at compile time instead of runtime.

However, one challenge we’ve faced with TypeScript in applying this approach is how to differentiate between values that have the same shape, but mean very different things. For example, if both my Person and my BlogPost have a numeric ID, I’d really like to communicate to TypeScript that they’re not interchangeable. But a function that takes a number accepts both kinds of values.

This post will examine the challenges one might face using the usual approach to this modeling problem, and how we’ve side-stepped them with a variation on the usual technique.
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Three Tips for Migrating from JavaScript to TypeScript

Over time, and especially in the past few years, the tech community has gotten sick of JavaScript and its loose typing. Trying to write a complicated program without static types is like driving at night without headlights—you’ll probably be fine for a while, but there’s a good chance you’ll crash a few times along the way. Read more on Three Tips for Migrating from JavaScript to TypeScript…

Understanding and Embracing TypeScript’s “readonly”

If you’ve tried to use JavaScript in a functional style, you’ve no doubt chafed at the fact that all those little objects flying around at any given time are about as far as they can possibly get from immutable. You can, of course, be careful to write code that never mutates an object, but while good practices improve your code, they’re weak defenses against bugs.

TypeScript can help you with its readonly property modifier. With readonly, you can rely on TypeScript’s static analysis to enforce and flag mutations in your codebase.
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A New Redux Action Pattern for TypeScript 2.4+

In September 2016, I wrote a post about a pattern for strongly typed Redux reducers in TypeScript. Since then, the TypeScript team has been busy enhancing the language, and recent changes in TypeScript have enabled a much more natural, boilerplate-free pattern for strongly typed actions and reducers in TypeScript.
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