TypeScript | Today I Learned

You can define primitive type aliases (e.g. string identifiers) in TypeScript that prevent you from using the wrong type using unique symbols:

type userId = string & {readonly id: unique symbol};

type projectId = string & {readonly id: unique symbol};

// A string can't just be assigned as a userId anymore, but this works.

const myUserId: userId = "u001" as userId;

// TS2322: Type 'userId' is not assignable to type 'projectId'. 🎉

const myProjectId: projectId = myUserId;

You can define a "collection" of TypeScript types using enums and interfaces, like this:

enum MyList {

  A,

  B,

  C

}

interface MyData {

  [MyList.A]: {color: string, enabled: boolean},

  [MyList.B]: string,

  [MyList.C]: any

}