npm package: @iotexproject/graphql-typed-client
Description: A tool that generates a strongly typed client library for any GraphQL endpoint. The client allows writing GraphQL queries as plain JS objects (with type safety, awesome code completion experience, custom scalar type mapping, type guards and more)
Author: helios1138
Latest version: 0.0.1

# graphql-typed-client [![npm version](https://img.shields.io/npm/v/graphql-typed-client.svg?style=flat-square)](https://www.npmjs.com/package/graphql-typed-client) [![Build Status](https://img.shields.io/travis/helios1138/graphql-typed-client/master.svg?style=flat-square)](https://travis-ci.org/helios1138/graphql-typed-client)

A tool that generates a strongly typed client library for any GraphQL endpoint. The client allows writing GraphQL queries
as plain JS objects (with type safety, awesome code completion experience, custom scalar type mapping, type guards and more)

#### Chain request syntax

![](https://i.gyazo.com/18e4670782b792f06c0e97abdee41bf2.gif)

#### Raw request syntax

![](https://i.gyazo.com/5f0255b59f0f9c7eebdbe6c077e39cb0.gif)

The request above is then converted to the GraphQL query and variables

```graphql
query Query($v1: String!, $v2: SearchType!, $v3: Int) {
  search(query: $v1, type: $v2, first: $v3) {
    nodes {
      ...f3
    }
  }
}
fragment f1 on User {
  name
}
fragment f2 on Organization {
  name
}
fragment f3 on Repository {
  name
  owner {
    ...f1
    ...f2
  }
}
```

```json
{ "v1": "graphql", "v2": "REPOSITORY", "v3": 5 }
```

## Install

```bash
yarn global add graphql-typed-client # needed for the CLI to work globally
yarn add graphql-typed-client # needed for the generated client to work
```

## Generate the client

To generate the client, use the CLI tool

```bash
generate-graphql-client
```

```bash
Usage: generate-graphql-client [options]

Options:
  -o, --output <./myClient>                    output directory
  -e, --endpoint <http://example.com/graphql>  GraphQL endpoint
  -p, --post                                   use POST for introspection query
  -s, --schema <./*.graphql>                   glob pattern to match GraphQL schema definition files
  -f, --fetcher <./schemaFetcher.js>           path to introspection query fetcher file
  -c, --config <./myConfig.js>                 path to config file
  -v, --verbose                                verbose output
  -h, --help                                   output usage information
```

If your endpoint is able to respond to introspection query without authentication, provide the `endpoint` option
(use `post` option to use POST request)

```bash
generate-graphql-client -e http://example.com/graphql -o myClient

# or using POST
generate-graphql-client -e http://example.com/graphql -p -o myClient
```

If your endpoint requires authentication or maybe some custom headers, use `fetcher` option to provide
a custom fetcher function.
We will pass [`fetch`](https://github.com/matthew-andrews/isomorphic-fetch) and [`qs`](https://github.com/ljharb/qs)
instances to your function for convenience, but you can use anything you like to fetch the introspection query

```bash
generate-graphql-client -f customFetcher.js -o myClient
```

```js
// customFetcher.js

module.exports = function(query, fetch, qs) {
  return fetch(`https://api.github.com/graphql?${qs.stringify({ query: query })}`, {
    headers: {
      Authorization: 'bearer YOUR_GITHUB_API_TOKEN',
    },
  }).then(r => r.json())
}
```

If instead of making a query to some endpoint, you just want to use a GraphQL schema definition, use `schema` option

```bash
generate-graphql-client -s mySchema.graphql -o myClient

# or
generate-graphql-client -s *.graphql -o myClient

# this will also work
generate-graphql-client -s "type User { name: String } type Query { users: [User] }" -o myClient
```

Alternatively, you can use a JS or JSON config file to define how you want the client to be generated.
Also, using the config file you can define more than one client.

The config file should contain an object or an array of objects, each representing a client to be generated.
Object fields are named the same way as the CLI arguments described above + `options` field
for passing various parsing/generation options (see [config.ts](src/config.ts) to learn more)

```bash
generate-graphql-client -c myConfig.js
```

```js
// myConfig.js

module.exports = [
  {
    schema: 'type Query { hello: String }',
    output: 'clients/simpleClient',
  },
  {
    schema: 'schemas/**/*.graphql',
    output: 'clients/clientFromSchema',
  },
  {
    endpoint: 'http://example.com/graphql',
    post: true,
    output: 'clients/exampleClient',
  },
  {
    fetcher: 'customFetcher.js',
    output: 'clients/customClient',
  },
  {
    fetcher: (query, fetch, qs) =>
      fetch(`https://api.github.com/graphql?${qs.stringify({ query })}`, {
        headers: {
          Authorization: 'bearer YOUR_GITHUB_API_TOKEN',
        },
      }).then(r => r.json()),
    output: 'clients/githubClient',
  },
]
```

## Create the client instance

To create the client instance, you have to call `createClient()` function that was generated with the client

If you want to execute Queries and Mutations, provide a `fetcher` function.

Just like with the fetcher that can be used for client generation, we will
pass [`fetch`](https://github.com/matthew-andrews/isomorphic-fetch) and [`qs`](https://github.com/ljharb/qs) instances
inside for convenience, but the function can be implemented in any way you want

If you want to execute Subscriptions, provide `subscriptionCreatorOptions` object with `uri` and `options` fields, where
`options` are `ClientOptions` passed down
to [`subscriptions-transport-ws`](https://github.com/apollographql/subscriptions-transport-ws)
(`reconnect` and `lazy` options are already enabled by default)

```js
// myClient.js

import { createClient } from './clients/myClient/createClient'

export const myClient = createClient({
  fetcher: ({ query, variables }, fetch, qs) =>
    fetch(`http://example.com/graphql?${qs.stringify({ query, variables })}`, {
      headers: {
        Authorization: 'bearer MY_TOKEN',
      },
    }).then(r => r.json()),
  subscriptionCreatorOptions: {
    uri: 'wss://example.com/graphql-subscriptions',
    options: {
      connectionParams: {
        token: 'MY_TOKEN',
      },
    },
  },
})
```

## Making GraphQL requests in JS

#### Raw request syntax

The format for the request object is visually similar to an actual GraphQL query, so something like

<!-- prettier-ignore -->
```js
query({
  user: [{ id: 'USER_ID' }, {
      username: 1,
      email: 1,
      on_AdminUser: {
        isSuperAdmin: 1,
      },
  }],
})
```

is easily recognizable as

```graphql
query {
  user(id: "USER_ID") {
    username
    email
    ... on AdminUser {
      isSuperAdmin
    }
  }
}
```

Here are the rules governing the format:

- fields with scalar types are written as

  `name: 1` or `name: true`

- fields with object types are written as JS objects

  `user: { name: 1 }`

- fields that have arguments are written as arrays with argument object and the field selection

  `user: [{ id: 'USER_ID' }, { name: 1 }]`

  - if the field has arguments, but the return type is scalar, just pass the array with argument object

    `userCount: [{ status: 'active' }]`

  - if all the arguments for the field are optional, you can omit the array and just pass the field selection

    `friend: { name: 1 }` is the same as `friend: [{}, { name: 1 }]`

- fields with `union` or `interface` types can have fragments defined on them to select fields of a specific type

  `on_AdminUser: { superAdmin: 1 }`

- **additionally**, there is a special `__scalar` field, that can be included in the field selection to automatically include
  all scalar fields from an object/interface type
  (excluding `__typename`, which you have to request manually if you need it)

  `user: { __scalar: 1 }`

Here is an example request object, showing all possible field types

<!-- prettier-ignore -->
```js
myClient.query({
  user: [{ id: 'USER_ID' }, {
    username: 1,
    email: 1,
    wasEmployed: [{ recently: true }],
    friends: {
      username: 1,
      email: 1,
    },
    posts: [{ limit: 5 }, {
      __scalar: 1,
    }],
    pets: {
      name: 1,
      on_Cat: {
        eyeColor: 1,
      },
      on_Snake: {
        length: 1,
      },
    },
  }],
})
```

When executed, it will send the following GraphQL `query` and `variables` to the server

```json
{ "v1": "USER_ID", "v2": true, "v3": 5 }
```

```graphql
query($v1: ID!, $v2: Boolean, $v3: Int) {
  user(id: $v1) {
    username
    email
    wasEmployed(recently: $v2)
    friends {
      username
      email
    }
    posts(limit: $v3) {
      ...f1
    }
    pets {
      name
      ...f2
      ...f3
    }
  }
}
fragment f1 on Post {
  id
  title
  content
}
fragment f2 on Cat {
  eyeColor
}
fragment f3 on Snake {
  length
}
```

#### Chain request syntax

```js
myClient.chain.query.user({ id: 'USER_ID' }).execute({
  username: 1,
  email: 1,
  on_AdminUser: {
    isSuperAdmin: 1,
  },
})

// execute() returns Promise<User> on query/mutation and Observable<User> on subscription
```

In the chain, each member refers to a GraphQL field going down the tree. Fields with arguments can be called like methods.
You can continue the chain so long as the fields that are mentioned are object types or interfaces (not arrays, unions etc.).
At any point, you can finish the chain by calling `execute(fieldRequest, defaultValue)`. Calling `execute()` returns
a `Promise` (for query/mutation) or an `Observable` (subscription) of type equal to the type of the last field in the chain.
Unlike in raw request syntax, where GraphQL errors are just returned in the response, chain execution will **throw** an error
if GraphQL endpoint responds with `errors`, empty `data` or empty value at the requested path when no `defaultValue`
was provided.

##### Default value logic clarification

```graphql
type User {
  status: String
}
```

```js
const status = await myClient.chain.query.user({ id: 'USER_ID' }).status.execute()
// status is `String | null`, which means that if user with specified ID exists, any string or null
// are both considered valid
// but if the user with specified ID is not found, the Promise returned from `execute()`
// will throw an error

const status = await myClient.chain.query.user({ id: 'USER_ID' }).status.execute(1, 'default status')
// in this case, if the user with specified ID is not found, returned status will be 'default status'
```

## Custom scalar type mapping

By default, all custom scalar types are generated as aliases to TypeScript's `any`

You can override this behavior by providing your own type mapper that will be used during the schema generation and applied
to query responses

For example, let's say you have a custom `Date` type. To specify how this type should be serialized/deserialized, create
a type mapper file (`.ts` or `.js`) somewhere in your app

```typescript
// path/to/typeMapper.ts

import moment, { Moment } from 'moment'

export const typeMapper = {
  Date: {
    serialize: (date: Moment) => date.toISOString(),
    deserialize: (date: string) => moment(date),
  },
}
```

Add `typeMapper` option to client generation config

```js
module.exports = {
  endpoint: 'http://example.com/graphql',
  output: 'clients/myClient',
  options: { typeMapper: { location: 'path/to/typeMapper', types: ['Date'] } },
}
```

Now, all fields of `Date` type in query responses will be automatically **deserialized**, and the return type of the
`deserialize()` function is going to be used as the definition for `Date` in generated TypeScript (enabling correct code
completion and type checking). All query variables of `Date` type and input object types that have `Date` fields will be
automatically **serialized** before sending.

<!-- prettier-ignore -->
```typescript
myClient
  .query({
    // `activatedAfter` is a `Date` argument, so now it accepts `Moment` instances
    user: [{ id: 'USER_ID', activatedAfter: moment('1999-01-01') }, {
      name: 1,
      birthday: 1,
    }],
  })
  .then(result => {
    if (!result.data) return
    const user = result.data.user

    // moment's methods are now available for `birthday` field in the response
    console.log(user.birthday.startOf('day').toISOString())
  })
```

## Type guards

Additionally, Typescript [type guard functions](https://www.typescriptlang.org/docs/handbook/advanced-types.html) are
generated for every object, interface and union type in your schema

<!-- prettier-ignore -->
```typescript
import { isCat, isSnake } from './clients/testClient/schema'

myClient
  .query({
    pet: [{ id: 'PET_ID' }, {
      name: 1,
      on_Cat: { eyeColor: 1 },
      on_Snake: { length: 1 },
    }],
  })
  .then(result => {
    if (!result.data) return
    const pet = result.data.pet

    console.log(pet.name) // pet type is abstract type Pet, so you only get access to shared fields

    if (isCat(pet)) {
      console.log(pet.eyeColor) // pet type is Cat, so you get access to fields of the specific type
    } else if (isSnake(pet)) {
      console.log(pet.length) // same here
    }
  })
```

## Notes on type annotation generation

- all known Scalar types are converted to their Typescript counterparts
- all unknown Scalar types are converted to type aliases for `any` unless type mapper is provided
- all Enum types are converted to Typescript enums, so you can import and use them in your code
  (even if you're not using Typescript)

## Notes on subscriptions

The generated client uses [Apollo](https://www.apollographql.com/)'s
[`subscriptions-transport-ws`](https://github.com/apollographql/subscriptions-transport-ws) for executing **Subscriptions**

Subscriptions are wrapped in [RxJs](https://github.com/ReactiveX/rxjs)' `Observable` which is chained
to the `SubscriptionClient` so that a connection is opened when you subscribe to the first subscription,
shared among all subscriptions and closed when you unsubscribe from the last one.