GraphQL Installation

Let's start with GraphQL.js installation. You must have the following things before going to start.

We need a computer system with running Windows, Linux, or macOS operating system. Here, we are using Windows.
We need the latest version of a web browser. Here, we recommend Google Chrome.
Install the latest version of Node.js. See how to install node.js: https://www.javatpoint.com/install-nodejs or go to node.js official website https://nodejs.org/en/ and download and install the latest version of node.js

There are two ways to execute GraphQL queries:

Execute GraphQL query with a command-line tool
Run an Express GraphQL Server to execute query

Execute GraphQL query with a command-line tool

Here, we are not using any language features that require transpilation, but we will use some ES6 features like Promises, classes, and fat arrow functions, etc.

Open node.js command prompt.
Run the following command to create a new project and install GraphQL.js.

npm init
npm install graphql --save

How to write the code?

There are three important components for GraphQL application. i.e. schema, query, and resolver. When we write a query for the GraphQL server, then to handle GraphQL queries, we need a schema. The schema is used to define the Query type. We also require an API root with a function called a "resolver" for each API endpoint.

Let's make an API to simple return "Hello World". Create a server.js file in the current folder where node.js is installed and write the following code:

var { graphql, buildSchema } = require('graphql');
// A schema is constructed 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! This is the first GrapghQL query';
  },
};

// Run the GraphQL query '{ hello }' and print out the response
graphql(schema, '{ hello }', root).then((response) => {
  console.log(response);
});

Now, run this using the following command:

Here, you can see the GraphQL response printed as

This is a simple GraphQL query that you executed on command prompt without using a server.

Run an Express GraphQL Server to execute query

The easiest way to run a GraphQL API server is to use Express. Express is a popular web application framework for Node.js.

If you have not installed Express yet, first install Express by using the following command

See this link for more information: https://www.javatpoint.com/install-expressjs

You have to install two additional dependencies by using the following command:

How to write the code?

Modify the "server.js" file with the following code to make an API server rather than a script that runs a single query. Here, we 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');

Now, run the GraphQL server by using the following command: