You can test this example on the TypeScript playground. Now when we pass a wrong type for any property of FilesReader (just like wrong types are being passed for the success and content properties), no error is thrown because conditionally, we’ve set the FilesReader type to any. To prevent this, we use conditional intersection via the union type, like so: type FilesReader = (Files & ErrorHandling) | any If for any reason a property with a type neither found in the Files type nor the ErrorHandling type is set, the TypeScript compiler throws an error. Here are two sets of numbers arranged in ascending order: D = ' Set theory provides the implicit concept that most of us use when thinking about union and intersection. Conditional intersection via union type.

Union and intersection types in TypeScript.Then, we’ll examine the definition and usage of the concept of union and intersection in TypeScript. First, we’ll look at the mathematical definition of these concepts used in set theory. In this article, we will explore the concept of union and intersection. Understanding the thought pattern behind the union and the intersection types in TypeScript helps you learn how better to implement them when necessary. Understanding discriminated union and intersection types in TypeScript He’s passionate about learning pure and applied mathematics concepts, open source, and software engineering. Logically, it shouldn't make a difference because boolean and Array are the same thing.Ikeh Akinyemi Follow Ikeh Akinyemi is a software engineer based in Rivers State, Nigeria. 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