Running an Express GraphQL Server

The simplest way to run a GraphQL API server is to use Express, a popular web application framework for Node.js. You will need to install two additional dependencies:

npm install express express-graphql graphql --save

Let's modify our “hello world” example so that it's an API server rather than a script that runs a single query. We can use the 'express' module to run a webserver, and instead of executing a query directly with the graphql function, we can use the express-graphql library to mount a GraphQL API server on the “/graphql” HTTP endpoint:

var express = require("express")
var { graphqlHTTP } = require("express-graphql")
var { buildSchema } = require("graphql")

// Construct a schema, using GraphQL schema language
var schema = buildSchema(`
  type Query {
    hello: String
  }
`)

// The root provides a resolver function for each API endpoint
var root = {
  hello: () => {
    return "Hello world!"
  },
}

var app = express()
app.use(
  "/graphql",
  graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true,
  })
)
app.listen(4000)
console.log("Running a GraphQL API server at http://localhost:4000/graphql")

You can run this GraphQL server with:

node server.js

Since we configured graphqlHTTP with graphiql: true, you can use the GraphiQL tool to manually issue GraphQL queries. If you navigate in a web browser to http://localhost:4000/graphql, you should see an interface that lets you enter queries. It should look like:

This screen shot shows the GraphQL query { hello } being issued and giving a result of { data: { hello: 'Hello world!' } }. GraphiQL is a great tool for debugging and inspecting a server, so we recommend running it whenever your application is in development mode.

At this point you have learned how to run a GraphQL server and how to use GraphiQL interface to issue queries. The next step is to learn how to issue GraphQL queries from client code.