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Last active Mar 18, 2018
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const express = require('express');
const graphqlHTTP = require('express-graphql'); // HTTP server middleware
const fetch = require('node-fetch'); // to perform our POST request
const DataLoader = require('dataloader'); // utility for batching and caching
const cors = require('cors'); // to set up cross-origin resource sharing
const schema = require('./schema'); // our data models
let app = express();
// Fetch data from the Pokemon API
const fetchPokemon = id =>
.then(response => response.json())
.catch(error => console.error(error));
// Optional for this demo, can comment out if don't need CORS enabled
let whitelist = [
let corsOptions = {
origin: function (origin, callback) {
let originIsWhitelisted = whitelist.indexOf(origin) !== -1;
callback(null, originIsWhitelisted);
credentials: true
// for now, redirect to localhost:3000/graphql
// eventually, can use the /graphql endpoint on front-end code
// (i.e in a componentDidMount method inside a React component to send
// a post request with desired fields)
app.get('/', (req, res, next) => {
// mount express-graphql as a route handler
app.use('/graphql', graphqlHTTP(req => {
// A batch loading function accepts an Array of keys
// and returns a Promise which resolves to an Array of values
const pokemonLoader = new DataLoader(keys =>
// config options
return {
schema, // from schema.js
context: {
pokemonLoader, // for batching, caching
graphiql: true // GraphiQL tool to manually issue GraphQL queries
const port = 3000;
console.log(`Listening on port ${port}. Go to /graphql to test out query backend.`);
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