Generics Explainer (an experiment)

00-response-mapping.ts

function createResponseMapper(responseType: string) {
  return (response) => {
    switch (responseType) {
      case "Game":
        return …;

      case "Post":
        return …;

      default:
        throw new TypeError(`Cannot map response of type ${responseType});
    }
  };
}

async function fetchAndMapData(url: string, responseType: string) {
  const data = await fetch(url).then((res) => res.json());
  return data.map(createResponseMapper(responseType));
}

fetchAndMapData(myPostApiUrl, "Post")
fetchAndMapData(myGameApiUrl, "Game")

generics-explainer.ts

function myFunction<T>(myArgument: T): T {
  if (typeof myArgument === "number") {
    return 42;
  }
  
  if (typeof myArgument === "string") {
    return "foo";
  }
  
  throw new TypeError(`I don't know how to handle "${typeof(myArgument)}"`);
}