The asserts syntax introduced with TS 3.7 allows us to interleave mutative runtime code with type annotations to express type mutations in a powerful way. This allows us to do away with the chaining syntax as described in my earlier article, Chained Tuple Types, and express our Set mutations in a much more familiar iterative way: const set: Set = new Set(); set.insert(2); set.insert(4); set.insert(8); set.remove(4); const hasResult1 = set.
The string deduplication problem is a canonical one within computer science, serving a similar purpose as fizz-buzz in terms of being an example of a simple problem that a reasonably knowledgable practitioner should be able to solve with minimal effort. The problem appears in a few variants, but briefly one such variant is to remove duplicate letters in a given string, such that the string then has only one instance of any given letter.
With Typescript 4.1, it’s now possible to use variadic tuple types to construct large types with what appears to be runtime code. The general idea is that we will utilize a chaining pattern, where each operation on the chain returns an expanded version of the chain’s type. To motivate the example, let us consider a Set class. Our Set is a chaining class, where you may insert, remove, and check for the existence of numbers.