custom apollo link to allow to parse custom scalars

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Custom Apollo Link to allow to parse custom scalars from responses, as well as serialize custom scalars in inputs. It can also validate enums, and cleanup __typename from inputs. (see Usage and Options).

Disclaimer: Potential cache interaction

Parsing scalars at link level means that Apollo cache will receive them already parsed. Depending on what kind of parsing is performed, this may interact with the cache JSON serialization of, for example,apollo-cache-persist. While apollo-cache-persist has an option to turn that serialisation off, others may have similar issues.

In the original Apollo Client Github issue thread about scalar parsing, this situation was discussed.

At the time of this writing, Apollo Client still does not support this over 4 years after the original ticket was opened. A potential solution of parsing after the cache might have some other issues, like returning different instances for the cached data, which may not be ideal in some situations that rely on that (e.g. react re-render control). I think some users will benefit more from the automatic parsing and serializing than the cost of the potential cache interactions.


yarn add apollo-link-scalars or npm install apollo-link-scalars.


We need to pass a GraphQLSchema, and optionally we can also pass a map of custom serialization/parsing functions for specific types.

You can build the link by calling the withScalars() function, passing to it the schema and optionally a typesMap.

import { withScalars } from "apollo-link-scalars";
import { ApolloLink } from "apollo-link";
import { HttpLink } from "apollo-link-http";
import { schema } from "./my-schema";

const link = ApolloLink.from([
  withScalars({ schema }),
  new HttpLink({ uri: "http://example.org/graphql" })

// we can also pass a custom map of functions. These will have priority over the GraphQLTypes parsing and serializing functions from the Schema.
const typesMap = {
  CustomScalar: {
    serialize: (parsed: CustomScalar) => parsed.toString(),
    parseValue: (raw: string | number | null): CustomScalar | null => {
      return raw ? new CustomScalar(raw) : null;

const link2 = ApolloLink.from([
  withScalars({ schema, typesMap }),
  new HttpLink({ uri: "http://example.org/graphql" })


We can pass extra options to withScalars() to modify the behaviour

  • removeTypenameFromInputs (Boolean, default false): when enabled, it will remove from the inputs the __typename if it is found. This could be useful if we are using data received from a query as an input on another query.
  • validateEnums (Boolean, default false): when enabled, it will validate the enums on parsing, throwing an error if it sees a value that is not one of the enum values.
  validateEnums: true,
  removeTypenameFromInputs: true

Example of loading a schema

import gql from "graphql-tag";
import { GraphQLScalarType, Kind } from "graphql";
import { makeExecutableSchema } from "graphql-tools";

// GraphQL Schema definition.
const typeDefs = gql`
  type Query {
    myList: [MyObject!]!

  type MyObject {
    day: Date
    days: [Date]!
    nested: MyObject

  "represents a Date with time"
  scalar Date

const resolvers = {
  // example of scalar type, which will parse the string into a custom class CustomDate which receives a Date object
  Date: new GraphQLScalarType({
    name: "Date",
    serialize: (parsed: CustomDate | null) => parsed && parsed.toISOString(),
    parseValue: (raw: any) => raw && new CustomDate(new Date(raw)),
    parseLiteral(ast) {
      if (ast.kind === Kind.STRING || ast.kind === Kind.INT) {
        return new CustomDate(new Date(ast.value));
      return null;

// GraphQL Schema, required to use the link
const schema = makeExecutableSchema({

Synchronously creating a link instance with graphql-code-generator setup

Warning: Be sure to watch your bundle size and know what you are doing.

Codegen config to generate introspection data:


      - "introspection"
      minify: true

Synchronous code to create link instance in common scenario:

import introspectionResult from "./__generated__/graphql.schema.json";
import { buildClientSchema, IntrospectionQuery } from "graphql";

const schema = buildClientSchema(introspectionResult)
// note: sometimes it seems to be needed to cast it as Introspection Query
// `const schema = buildClientSchema((introspectionResult as unknown) as IntrospectionQuery)`

const scalarsLink = withScalars({
  typesMap: { … },


The link code is heavily based on apollo-link-response-resolver by will-heart.

While the approach in apollo-link-response-resolver is to apply resolvers based on the types taken from __typename, this follows the query and the schema to parse based on scalar types. Note that apollo-link-response-resolver is archived now

I started working on this after following the Apollo feature request https://github.com/apollographql/apollo-feature-requests/issues/2.

Development, Commits, versioning and publishing

See documentation for development

See The Typescript-Starter docs.

Commits and CHANGELOG

For commits, you should use commitizen

yarn global add commitizen

#commit your changes:
git cz

As typescript-starter docs state:

This project is tooled for conventional changelog to make managing releases easier. See the standard-version documentation for more information on the workflow, or CHANGELOG.md for an example.

# bump package.json version, update CHANGELOG.md, git tag the release
yarn run version

You may find a tool like wip helpful for managing work in progress before you're ready to create a meaningful commit.

Creating the first version

Once you are ready to create the first version, run the following (note that reset is destructive and will remove all files not in the git repo from the directory).

# Reset the repo to the latest commit and build everything
yarn run reset && yarn run test && yarn run doc:html

# Then version it with standard-version options. e.g.:
# don't bump package.json version
yarn run version -- --first-release

# Other popular options include:

# PGP sign it:
# $ yarn run version -- --sign

# alpha release:
# $ yarn run version -- --prerelease alpha

And after that, remember to publish the docs.

And finally push the new tags to github and publish the package to npm.

# Push to git
git push --follow-tags origin master

# Publish to NPM (allowing public access, required if the package name is namespaced like `@somewhere/some-lib`)
yarn publish --access public

Publish the Docs

yarn run doc:html && yarn run doc:publish

This will generate the docs and publish them in github pages.

Generate a version

There is a single yarn command for preparing a new release. See One-step publish preparation script in TypeScript-Starter

# Prepare a standard release
yarn prepare-release

# Push to git
git push --follow-tags origin master

# Publish to NPM (allowing public access, required if the package name is namespaced like `@somewhere/some-lib`)
yarn publish --access public

Contributors ✨

Thanks goes to these wonderful people (emoji key):

Eduardo TuriΓ±o

πŸ€” πŸš‡ ⚠️ πŸ’» πŸ“–

Genadi Samokovarov

πŸ› ⚠️ πŸ’»

JiΕ™Γ­ Brabec

πŸ“– πŸ› ⚠️ πŸ’» πŸ€”

Jakub Petriska


This project follows the all-contributors specification. Contributions of any kind welcome!