Farfetch GraphQL fragments plugin

farfetch-graphql.js

const graphQLFragments = (fragments = {}) => req => {
  const uniq = list => list.filter(value => list.indexOf(value) == list.lastIndexOf(value));
  const hasFragment = graphQL => graphQL.match(/\.{3}\s*([A-Za-z0-9\_]+)/g) != null;
  const findFragments = graphQL =>
    graphQL
      .match(/\.{3}\s*([A-Za-z0-9\_]+)/g)
      .map(fragment => fragment.trim().replace(/^\.{3}/, ""))
      .filter(fragment => fragment.match(/\s+on\s+/) == null)
      .map(fragment => {
        if (fragment in fragments) {
          return hasFragment(fragments[fragment]) ?
            [...findFragments(fragments[fragment]), fragment] :
            [fragment];
        } else {
          throw new Error(`GraphQL: Fragment ${fragment} not found.`);
        }
      })
      .reduce((all, current) => [current, ...all]);

  const appendedFragments = uniq(findFragments(req.body.query))
    .map(fragment => `fragment ${fragment} on ${fragments[fragment]}`)
    .join("");

  return {
    ...req,
    body: {
      ...req.body,
      query: req.body.query + appendedFragments,
    },
  };
};

usage.js

const graphAPI = farfetch
  .post("http://api.graph.ql")
  .set("Content-Type", "application/json")
  .use(graphQLFragments({
    user: "User { id, name, posts { ...post } }",
    post: "Post { id, body }",
  }))
  .use(req => ({ ...req, body: JSON.stringify(req.body) }))
  .use((req, execute) => execute(req).then(res => res.json()));

const graph = (query, variables = {}) => graphAPI.send({ query, variables });

const user = graph("query user($userId: ID!) { findUser(id: $userId) { ...user } }", { userId: "10" });