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 graphql-http 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 graphql-http library to mount a GraphQL API server on the “/graphql” HTTP endpoint:

var express = require('express');
var { createHandler } = require('graphql-http/lib/use/express');
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();
 
// Create and use the GraphQL handler.
app.all(
  '/graphql',
  createHandler({
    schema: schema,
    rootValue: root,
  }),
);
 
// Start the server at port
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

Using GraphiQL

GraphiQL is GraphQL’s IDE; a great way of querying and exploring your GraphQL API. One easy way to add it to your server is via the MIT-licensed ruru package which bundles a prebuilt GraphiQL with some popular enhancements. To do so, install the ruru module with npm install --save ruru and then add the following to your server.js file, then restart the node server.js command:

var { ruruHTML } = require('ruru/server');
 
// Serve the GraphiQL IDE.
app.get('/', (_req, res) => {
  res.type('html');
  res.end(ruruHTML({ endpoint: '/graphql' }));
});

If you navigate to http://localhost:4000, you should see an interface that lets you enter queries; now you can use the GraphiQL IDE tool to issue GraphQL queries directly in the browser.

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