Pack and unpack JSON value

pack.ts

export function packJSON(object: unknown) {
  const fragments: object[] = [];
  const indices = new Map<string, number>();
  function next(node: unknown): unknown {
    if (node && typeof node === "object") {
      let fragment: object;
      if (Array.isArray(node)) {
        fragment = node.map((el) => next(el));
      } else {
        fragment = Object.entries(node).reduce<Record<string, unknown>>((obj, [key, value]) => {
          obj[key] = next(value);
          return obj;
        }, {});
      }
      const id = JSON.stringify(fragment);
      let index = indices.get(id);
      if (index !== undefined) return `#<${index}>`;
      index = fragments.push(fragment) - 1;
      indices.set(id, index);
      return `#<${index}>`;
    }
    return node;
  }
  next(object);
  return fragments;
}

unpack.ts

const pattern = /^#\<\d+\>$/;

function next(node: unknown, context: unknown[]): unknown {
  switch (typeof node) {
    case "string":
      if (pattern.test(node)) {
        const index = Number.parseInt(node.slice(2, -1));
        return next(context[index], context);
      }
      return node;
    case "object":
      if (node === null) {
        return null;
      }
      if (Array.isArray(node)) {
        return node.map((el) => next(el, context));
      }
      return Object.keys(node)
        .sort()
        .reduce<Record<string, unknown>>((obj, key) => {
          const value = (node as Record<string, unknown>)[key];
          obj[key] = next(value, context);
          return obj;
        }, {});
    default:
      return node;
  }
}

export function unpackJSON(data: unknown[]) {
  return next(data[data.length - 1], data);
}