In many editors we can observe these types as they change, and we’ll even do so in our examples. It looks at these special checks (called type guards) and assignments, and the process of refining types to more specific types than declared is called narrowing. TypeScript follows possible paths of execution that our programs can take to analyze the most specific possible type of a value at a given position. Within our if check, TypeScript sees typeof padding = 'number' and understands that as a special form of code called a type guard. Much like how TypeScript analyzes runtime values using static types, it overlays type analysis on JavaScript’s runtime control flow constructs like if/else, conditional ternaries, loops, truthiness checks, etc., which can all affect those types. While it might not look like much, there’s actually a lot going under the covers here. The idea is that TypeScript’s type system aims to make it as easy as possible to write typical JavaScript code without bending over backwards to get type safety. Logically, it shouldn't make a difference because boolean and Array are the same thing.If this mostly looks like uninteresting JavaScript code, that’s sort of the point.Īpart from the annotations we put in place, this TypeScript code looks like JavaScript. I tried with TypeScript 2.1.4 the suggested fix of replacing boolean with Array. This adds the necessary declaration of includes on arrays. As far as fixing the compilation error goes, fixed the compilation issue was adding es2016 to the lib option in my tsconfig.json.

Typescript includes