What is the difference between WebSockets and HTTP?

Expected Interview Answer

Step-by-Step Explanation

1. Step 1

   Compare the connection model

   HTTP opens short-lived request-response exchanges; WebSockets keep one persistent connection open.

2. Step 2

   Compare direction

   HTTP is client-initiated one-way per exchange; WebSockets are full-duplex, either side can send anytime.

3. Step 3

   Compare overhead

   HTTP sends full headers per request; WebSocket frames are tiny after the initial handshake.

4. Step 4

   Compare state

   HTTP is stateless by design; a WebSocket connection is stateful and long-lived.

5. Step 5

   Pick the right tool

   Use HTTP for fetching resources and REST APIs; use WebSockets for continuous real-time bidirectional data.

Code Example

// HTTP: one request, one response, then done
const res = await fetch('https://example.com/api/prices')
const prices = await res.json()

// WebSocket: open once, receive many pushes over time
const socket = new WebSocket('wss://example.com/prices')
socket.onmessage = (event) => {
  console.log('Pushed update:', JSON.parse(event.data))
}

Follow-up Questions

• When would you still prefer HTTP over WebSockets?
• How does the WebSocket handshake reuse HTTP?
• What is HTTP long-polling and how does it compare?
• How do Server-Sent Events differ from WebSockets?
• Can WebSockets and HTTP share the same port?