Difficulties With Dictionaries In TypeScript

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topic: [🦒 TypeScript]
links: What is TypeScript
source: TypeScript course by the native web
tags: #permanent-note #published

Last Modified: =dateformat(this.file.mtime, "MMM. dd, yyyy - HH:mm")

Defining dictionaries in TypeScript can be a bit complicated because the type system gets in the way. Here are some examples of how not to do it.
Imagine a dictionary of country populations.

// Doesn't work, because empty object does not allow accessing properties.
let countries = {};
countries.germany = 80_000_000;

// Doesn't work, because object does not allow accessing properties.
let countries: object = {};
countries.germany = 80_000_000;

// Doesn't work, because Object does not allow accessing properties.
let countries: Object = {};
countries.germany = 80_000_000;

// Works, but is not very well extensible.
interface Countries {
  germany?: number;
  france?: number;
}
let countries: Countries = {};
countries.germany = 80_000_000;
countries.france = 66_000_000;

// Works, but accessing a property leads to always-existent values, no matter whether they have been defined or not.
interface Countries {
  [ name: string ]: number;
}
let countries: Countries = {};
countries.germany = 80_000_000;
countries.france = 66_000_000;
countries.italy = 60_000_000;

// so this is the way
let countries: Record<string, unknown> = {};
countries.germany = 80_000_000;
countries.france = 66_000_000;