utility-types

utility-types

Exploring TypeScript's utility types which enable powerful type designs using type transformations.

Overview

TypeScript's type system is one of the most feature-rich among programming languages. One facet of this is in the utility types like Partial, Omit, Exclude, Extract, Parameters, etc. The core idea with these is to reference some type and transform it into a new type. For me, this is hard to grasp. I'd like to learn and explore these utility types by way of runnable example programs.

Instructions

Follow these instructions to build and run the program.

1. Pre-requisite: Node.js
   • I used version 20.11.0
2. Install dependencies

   • npm install

3. Compile the TypeScript source code into JavaScript

   • npm run build

   • Notice the dist/utility-types.js file.
4. Run the program

   • node dist/utility-types.js

   • The output will look like this:

     Style #1: Invoke the function and inline the argument.
     The function was called with the 'foo' form. foo=Hello
     The function was called with the 'bar/baz' form. bar=hi, baz=1
     Style #2: Declare a variable for the argument ahead of time.
     The function was called with the 'foo' form. foo=Hello
     Style #3: Declare a variable for the argument ahead of time and specify the type explicitly.
     The function was called with the 'bar/baz' form. bar=hi, baz=1
     Style #4: Use the 'Parameters' utility type to reference the function signature.
     The function was called with the 'foo' form. foo=Hello
     The function was called with the 'bar/baz' form. bar=hi, baz=1
     

Reference

• TypeScript handbook: Parameters

  • Constructs a tuple type from the types used in the parameters of a function type Type.