typescript+matchtypescriptmatch

match consumer examples

How a TypeScript app uses @danrabydev/match ^0.3.1: exhaustive Status.match, one ApiResult namespace, peek-then-match, merge, and diagnostics on Error. No _ hatch.

August 24, 2026

typescriptapp/src/page.ts

import { type TagMismatch } from "@danrabydev/match";
import {
  ApiResult,
  getPost,
  getUser,
  interceptErrors,
  type ApiError,
} from "./api.js";

function isTagMismatch(err: unknown): err is TagMismatch {
  return (
    typeof err === "object" &&
    err !== null &&
    "reason" in err &&
    err.reason === "tag-mismatch"
  );
}

export function loadPage(userId: string, postId: string) {
  return ApiResult.merge(getUser(userId), getPost(postId));
}

export function handlePage(result: ReturnType<typeof loadPage>): string {
  ApiResult.peek(result, interceptErrors);
  return ApiResult.match(result, {
    Idle: () => "idle",
    Loading: ({ msg }) => msg.join(", "),
    Success: ({ data: [user, post] }) => `${user.name}: ${post.title}`,
    Error: ({ err }) => {
      if (isTagMismatch(err)) return `mismatch: ${err.tags.join(",")}`;
      const [first] = err as ApiError[];
      if (first === undefined) return "error";
      return `${first.code}: ${first.message}`;
    },
    Cached: ({ at }) => at[0]?.toISOString() ?? "",
  });
}

handlePage(loadPage("1", "9"));
// => "ada: notes"