What are typeDefs in GraphQL?

typeDefs are what defines the schema of your GraphQL API.

typeDefs are usually a string or an array of GraphQL domain specific language strings or a function that takes no arguments and returns an array of graphQL schema language strings. The order of the strings is not important, but there must be a schema definition, except in this example below where we are introducing ourselves to the typeDefs via a simple query for information on the graphQL API. [source][https://www.apollographql.com/docs/graphql-tools/generate-schema.html#schema-language]

//index.js
const { GraphQLServer } = require('graphql-yoga')

const typeDefs = `
   type Query{ 
        info: String!
    }`

Let’s break down what’s happening in this code.

First we are making our file require graphql-yoga, which has the following set of features:

-GraphQL spec-compliant -Supports file upload -Realtime functionality with GraphQL subscriptions -Works with TypeScript typings -Out-of-the-box support for GraphQL Playground -Extensible via Express middlewares -Resolves custom directives in your GraphQL schema -Query performance tracing -Accepts both application/json and application/graphql content-types -Runs everywhere: Can be deployed via now, up, AWS Lambda, Heroku etc.

With this, we will be able to instantiate a new const called server in the file, but we will only be covering the first part of the introductory code in this file, the typeDefs (spoiler alert: there are three types of consts in t index.js file)

Second, we are defining the typeDefs with the const typeDefs code. We do this by first defining the const typeDefs = and by adding a back tick to indicate the schema of the graphQL API. graphQL APIs have three different types of special root types query, mutation, and subscription.

In this example, we are using the query special root type in our root field where we define what type of operations are available to us in the graphQL API. So, we define this with type Query, then specify that it has one field called info, which is a string with String! and the ! indicates that it cannot be null.

With only one root field, only one type of query is accepted by the API, right now, that is the

    query {
        info
    }

entered into the graphQL playground command that corresponds to the typeDef set in the graphQL index.js file.

For a full stack tutorial on building your own Hackernews Clone GraphQL API, [visit here][https://www.howtographql.com/graphql-js/0-introduction/]

For more information on GraphQL as a whole,[visit here][https://www.howtographql.com/graphql-js/1-getting-started/]