<p><a href="https://graphql.org/" rel="noopener noreferrer" target="_blank">GraphQL</a> is an application layer server-side technology that is developed by Facebook for executing queries with existing data. GraphQL can optimize RESTful API calls. It gives a declarative way of fetching and updating your data. GraphQL helps you to load data from server to client. It enables programmers to choose the types of requests they like to make. It provides us with a more efficient way to design, create, and consume our APIs. Basically, it’s the replacement for REST.</p><h2><br></h2><h2>Features</h2><ul><li>It provides declarative query language, which is not imperative.</li><li>It is hierarchical and product-centric.</li><li>GraphQL is strongly typed. It means queries are executed within the context of a particular system.</li><li>Queries in GraphQL are encoded in the client, not in the server.</li><li>It has all the features of the application layer of the OSI model.</li><li>Write the data that you want, and you get exactly the data that you want.</li><li>No more over-fetching of information as we are used to with REST.</li><li>Single endpoint, no more version 2 or version 3 for the same API.</li></ul><p><br></p><h2>Why use?</h2><ul><li>It provides a human-readable query.</li><li>It is very easy to deal with many databases.</li><li>It is suited for microservices and complex systems.</li><li>You can fetch data with a single API call.</li><li>It helps you with query batching and caching.</li><li>You do not face, over, and under-fetching problems.</li><li>Tailoring requests to your needs.</li><li>It helps you to discover the schema in the appropriate format.</li><li>GraphQL automatically keeps documentation in sync with API changes.</li><li>API evolution is possible without versioning.</li><li>GraphQL fields are used in multiple queries that can be shared to a higher component level for reuse.</li><li>You can choose which functions to expose and how they work.</li><li>It can be used for rapid application prototyping.</li></ul><h2><br></h2><h2>Applications</h2><ul><li>It provides Relay and other client frameworks</li><li>Graphql helps you to improve the performance of the mobile app.</li><li>It can reduce the over-fetching problems to lower server-side cloud service and decrease the client-side, network usage.</li><li>It can be used when the client application has to specify which fields are needed in long query format.</li><li>Graphql can be fully utilized when you have to add functionality to your old or existing API.</li><li>It is used when you have to simplify complex API.</li><li>Mix and mash pattern, which is commonly used in object-oriented programming.</li><li>When you have to aggregate data from more than one place into one convenient API.</li><li>You can use GraphQL as an abstraction on an existing API to specify a response structure based on user needs.</li></ul><p><br></p><h2>Simple graphQL server Example</h2><p>We should install a graphql npm package. Copy the below command and paste it to your terminal:</p><pre class="ql-syntax" spellcheck="false"><span class="hljs-built_in">npm</span> install graphql
</pre><p>Below is a sample server with graphQL and Node.js. Copy the below code into a file called server.js or any file with .js extension.</p><p><br></p><pre class="ql-syntax" spellcheck="false">var { graphql, buildSchema } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'graphql'</span>);
 
var schema = buildSchema(`
  type Query {
    <span class="hljs-attr">hello</span>: <span class="hljs-built_in">String</span>
  }
`);
 
var root = { hello: <span class="hljs-function"><span class="hljs-params">()</span> =&gt;</span> <span class="hljs-string">'Hello world!'</span> };
 
graphql(schema, <span class="hljs-string">'{ hello }'</span>, root).<span class="hljs-keyword">then</span>(<span class="hljs-function"><span class="hljs-params">(response)</span> =&gt;</span> {
  <span class="hljs-built_in">console</span>.log(response);
});
</pre><p><br></p><p>Run the server file with:</p><pre class="ql-syntax" spellcheck="false">node server.js
</pre><p>You'll see the below output:</p><pre class="ql-syntax" spellcheck="false">{ <span class="hljs-attribute">data</span>: { hello: <span class="hljs-string">'Hello world!'</span> } }
</pre><p><br></p><p>Happy coding ...</p>

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