I had my first "I wish this was Typescript moment" this week. I was working on a script that takes the output from a turbo --dry=json run and groups the packages into shards. This is mostly irrelevant, but I was creating some simple objects with properties and then add/removing props as I got more information. For example:

[
  {
    "pkg": "foo",
    "directory": "packages/foo"
  },
  // ...
];

turned into

[
  {
    pkg: "foo",
    directory: "packages/foo",
+    services: {}
  },
  // ...
];

and so on.

As I was iterating on this code, it became really annoying to remember what properties I had or didn't have and whether or not they could be null or undefined at any given moment.

I added types to my data structure and completely solved the problem.

interface PackageInfo {
  pkg: string;
  directory: string;
}

// adds in another field
interface DecoratedPackageInfo extends PackageInfo {
  other: Record<string, string>;
}

// drops directory
type UsefulPackageInfo = Omit<DecoratedPackageInfo, "directory">;