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Lesson 1 of 7 · 10 min · 1 hands-on step

HTTP: Requests & Responses

The language browsers and servers speak, taken apart line by line.

A conversation in plain text

When you open a page, your browser sends a request like this:

GET /courses HTTP/1.1
Host: crayoninterview.com
Accept: text/html
Cookie: session=abc123

And the server sends back a response:

HTTP/1.1 200 OK
Content-Type: text/html
Cache-Control: max-age=60

<!doctype html><html>…

That's HTTP: a request line (or status line), headers (extra details), a blank line, then an optional body.

Methods: what you want to do

Method Meaning Example
GET read load a page or a list of courses
POST create sign up, add a comment
PUT / PATCH replace / update edit your profile
DELETE remove delete a post

Status codes: how it went

Range Meaning Common ones
2xx success 200 OK, 201 Created, 204 No Content
3xx go elsewhere 301 Moved, 304 Not Modified
4xx you (the client) made a mistake 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 429 Too Many Requests
5xx the server broke 500 Internal Server Error, 503 Unavailable

Try it in the browser

Open DevTools (right-click → Inspect) on any site, go to the Network tab, and reload. Every line is a request. Click one to see its method, status, headers and response. You'll use this tab almost every day as a web developer.

JavaScript · try it
const url = new URL("https://crayoninterview.com/courses?page=2&sort=new");
console.log(url.pathname, Object.fromEntries(url.searchParams));

🧪 Practice

Raw HTTP requests are just text. Write parseRequest(raw) that returns { method, path, headers } where headers is an object with lowercase header names.

The first line looks like GET /courses?page=2 HTTP/1.1, then one Name: value header per line.

JavaScript
function parseRequest(raw) {
  const lines = raw.split("\n");
  return { method: "", path: "", headers: {} };
}

Output appears here. Press Run or Ctrl/⌘ + Enter.

✅ Check your understanding

  1. Which status code means "Not Found"?

  2. Which HTTP method should never change data on the server?

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