Web APIs are interfaces that allow web applications to communicate with external services or data sources over the internet.

1. REST API

• REST APIs use standard HTTP methods & are stateless. They
  typically return data in JSON or XML format.

• Used for web services, where resources are accessed via URLs. Commonly used for CRUD operations on data.

• Example: GitHub API, Twitter API.
  

fetch('https://api.github.com/users/octocat')
    .then(responce => responce.json())
    .then(data => console.log(data))
    .catch(error => console.error('Error:', error));

2. SOAP API

• SOAP is a protocol that uses XML for message format & typically relies on HTTP or SMTP for message negotiation & transmission.

• Enterprise-level applications requiring security, reliability, and
  formal contracts (WSDL).

• Example: Payment gateways, financial services APIs.
  

const soap = require('soap');
const url = 'https://www.example.com/service?wsdl';
soap.createClient(url, (err, client) => {
    if (err) throw err;
    client.MyFunction({ param: 'value' }, (err, result) => {
        if (err) throw err;
        console.log(result);
    });
});

3. GraphQL API

• GraphQL allows clients to request exactly the data they
  need, and nothing more. It uses a single endpoint and
  provides more flexibility compared to REST.

• When you need efficient querying of complex datasets, or when working with mobile applications where bandwidth
  is a concern.

• Example: Facebook's GraphQL API, Shopify API.
  

const { request, gql } = require('graphql-request');
const query = gql`
    {
        user(login: "octocat"){
            name
            bio
        }
    }
`;

request('https://api.github.com/graphql', query)
    .then(data => console.log(data))
    .catch(error => console.error('Error:', error));

4. WebSocket API

• WebSocket's enable real-time, two-way communication between client and server over a single, long-lived connection.

• Real-time applications like chat applications, live sports updates, and online games.

• Example: Slack API, trading platforms.
  

const socket = new WebSocket('wss://example.com/socket');
socket.onopen = ()=>{
    console.log('Connected');
    socket.send(JSON.stringify({type: 'follow', channel: 'news'}));
};

socket.onmessage = event =>{
    console.log('Message from server', event.data);
};

socket.onclose = () =>{
    console.log('Disconnected');
}

5. OAuth API

• OAuth is a protocol that allows third-party applications to grant limited access to user accounts on an HTTP service, typically used for authentication and authorization.

• Used for single sign-on (SSO) and authorization across different services.

• Example: Google OAuth 2.0, Facebook Login API
  

const axios = require('axios');
const token = 'your_oauth_token';
axios.get('https://api.example.com/userinfo', {
    headers: { Authorization: `Bearer ${token}` }
})
    .then(responce => console.log(responce.data))
    .catch(error => console.error('Error:', error));

6. Batch API

• Batch APIs allow clients to make multiple API calls in a single HTTP request, often improving performance by reducing the number of network requests.

• When a client needs to perform multiple actions at once or when working with large datasets.

• Example: Facebook Graph API batch requests
  

fetch('https://graph.facebook.com/v11.0', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
        batch: [
            { method: 'GET', relative_url: 'me' },
            { method: 'GET', relative_url: 'me/friends' }
        ],
        access_token: 'your_access_token'
    })
})
    .then(responce => responce.json())
    .then(data => console.log(data))
    .catch(error => console.error('Error:', error));