graphql-tag

What is graphql-tag?

The graphql-tag npm package is primarily used for parsing GraphQL queries and fragments into a standard GraphQL AST (Abstract Syntax Tree). It is commonly used in JavaScript or TypeScript projects that interact with a GraphQL server. The package provides a simple and efficient way to embed GraphQL queries within the code.

What are graphql-tag's main functionalities?

Parsing GraphQL queries

This feature allows developers to write GraphQL queries inside JavaScript or TypeScript files using template literals. The gql function parses the query string into a GraphQL AST, which can then be used with GraphQL clients like Apollo Client.

import gql from 'graphql-tag';

const MY_QUERY = gql`
  query GetUserInfo($userId: ID!) {
    user(id: $userId) {
      id
      name
      email
    }
  }
`;

Parsing GraphQL fragments

This feature allows the definition of GraphQL fragments that can be reused across multiple queries or mutations. The gql function is used to parse the fragment, and it can be embedded within queries or mutations to avoid repetition of field definitions.

import gql from 'graphql-tag';

const USER_FRAGMENT = gql`
  fragment UserFragment on User {
    id
    name
    email
  }
`;

const MY_QUERY = gql`
  query GetUserInfo($userId: ID!) {
    user(id: $userId) {
      ...UserFragment
    }
  }
  ${USER_FRAGMENT}
`;

Support for multiple operations in a single document

graphql-tag supports defining multiple operations, such as queries and mutations, within a single gql template literal. This can be useful for organizing related operations together in one place.

import gql from 'graphql-tag';

const MULTIPLE_OPERATIONS = gql`
  query GetUserInfo($userId: ID!) {
    user(id: $userId) {
      id
      name
    }
  }

  mutation UpdateUserName($userId: ID!, $newName: String!) {
    updateUser(id: $userId, name: $newName) {
      id
      name
    }
  }
`;

Other packages similar to graphql-tag

graphql

The 'graphql' package is the core JavaScript implementation of GraphQL itself. It includes functionality for parsing queries, but it's more general-purpose and lower-level compared to graphql-tag. It does not provide the same template literal syntax for embedding queries.

apollo-boost

Apollo Boost is a package that includes graphql-tag as one of its dependencies. It provides a zero-config way to start using Apollo Client. It's more of a complete solution for managing GraphQL state in applications, whereas graphql-tag is focused solely on parsing queries.

graphql.macro

graphql.macro provides similar functionality to graphql-tag but is designed to work with Create React App without ejecting. It allows you to load .graphql and .gql files at compile time, which graphql-tag does not do by default.

README

graphql-tag

Helpful utilities for parsing GraphQL queries. Includes:

• gql A JavaScript template literal tag that parses GraphQL query strings into the standard GraphQL AST.
• /loader A webpack loader to preprocess queries

graphql-tag uses the reference graphql library under the hood as a peer dependency, so in addition to installing this module, you'll also have to install graphql.

gql

The gql template literal tag can be used to concisely write a GraphQL query that is parsed into a standard GraphQL AST. It is the recommended method for passing queries to Apollo Client. While it is primarily built for Apollo Client, it generates a generic GraphQL AST which can be used by any GraphQL client.

import gql from 'graphql-tag';

const query = gql`
  {
    user(id: 5) {
      firstName
      lastName
    }
  }
`

The above query now contains the following syntax tree.

{
  "kind": "Document",
  "definitions": [
    {
      "kind": "OperationDefinition",
      "operation": "query",
      "name": null,
      "variableDefinitions": null,
      "directives": [],
      "selectionSet": {
        "kind": "SelectionSet",
        "selections": [
          {
            "kind": "Field",
            "alias": null,
            "name": {
              "kind": "Name",
              "value": "user",
              ...
            }
          }
        ]
      }
    }
  ]
}

Fragments

The gql tag can also be used to define reusable fragments, which can easily be added to queries or other fragments.

import gql from 'graphql-tag';

const userFragment = gql`
  fragment User_user on User {
    firstName
    lastName
  }
`

The above userFragment document can be embedded in another document using a template literal placeholder.

const query = gql`
  {
    user(id: 5) {
      ...User_user
    }
  }
  ${userFragment}
`

Note: While it may seem redundant to have to both embed the userFragment variable in the template literal AND spread the ...User_user fragment in the graphQL selection set, this requirement makes static analysis by tools such as eslint-plugin-graphql possible.

Why use this?

GraphQL strings are the right way to write queries in your code, because they can be statically analyzed using tools like eslint-plugin-graphql. However, strings are inconvenient to manipulate, if you are trying to do things like add extra fields, merge multiple queries together, or other interesting stuff.

That's where this package comes in - it lets you write your queries with ES2015 template literals and compile them into an AST with the gql tag.

Caching parse results

This package only has one feature - it caches previous parse results in a simple dictionary. This means that if you call the tag on the same query multiple times, it doesn't waste time parsing it again. It also means you can use === to compare queries to check if they are identical.

Importing graphQL files

To add support for importing .graphql/.gql files, see Webpack loading and preprocessing below.

Given a file MyQuery.graphql

query MyQuery {
  ...
}

If you have configured the webpack graphql-tag/loader, you can import modules containing graphQL queries. The imported value will be the pre-built AST.

import MyQuery from 'query.graphql'

Importing queries by name

You can also import query and fragment documents by name.

query MyQuery1 {
  ...
}

query MyQuery2 {
  ...
}

And in your JavaScript:

import { MyQuery1, MyQuery2 } from 'query.graphql'

Preprocessing queries and fragments

Preprocessing GraphQL queries and fragments into ASTs at build time can greatly improve load times.

Babel preprocessing

GraphQL queries can be compiled at build time using babel-plugin-graphql-tag. Pre-compiling queries decreases script initialization time and reduces bundle sizes by potentially removing the need for graphql-tag at runtime.

TypeScript preprocessing

Try this custom transformer to pre-compile your GraphQL queries in TypeScript: ts-transform-graphql-tag.

React Native and Next.js preprocessing

Preprocessing queries via the webpack loader is not always possible. babel-plugin-import-graphql supports importing graphql files directly into your JavaScript by preprocessing GraphQL queries into ASTs at compile-time.

E.g.:

import myImportedQuery from './productsQuery.graphql'

class ProductsPage extends React.Component {
  ...
}

Webpack loading and preprocessing

Using the included graphql-tag/loader it is possible to maintain query logic that is separate from the rest of your application logic. With the loader configured, imported graphQL files will be converted to AST during the webpack build process.

Example webpack configuration

{
  ...
  loaders: [
    {
      test: /\.(graphql|gql)$/,
      exclude: /node_modules/,
      loader: 'graphql-tag/loader'
    }
  ],
  ...
}

Create React App

Preprocessing GraphQL imports is supported in create-react-app >= v2 using evenchange4/graphql.macro.

For create-react-app < v2, you'll either need to eject or use react-app-rewire-inline-import-graphql-ast.

Testing

Testing environments that don't support Webpack require additional configuration. For Jest use jest-transform-graphql.

Warnings

This package will emit a warning if you have multiple fragments of the same name. You can disable this with:

import { disableFragmentWarnings } from 'graphql-tag';

disableFragmentWarnings()

Experimental Fragment Variables

This package exports an experimentalFragmentVariables flag that allows you to use experimental support for parameterized fragments.

You can enable / disable this with:

import { enableExperimentalFragmentVariables, disableExperimentalFragmentVariables } from 'graphql-tag';

Enabling this feature allows you declare documents of the form

fragment SomeFragment ($arg: String!) on SomeType {
  someField
}

Resources

You can easily generate and explore a GraphQL AST on astexplorer.net.