Lesson 1 of 6 · About 6 minutes
Follow a request from browser to server
Learn the concept.
A page can feel like one object, but loading it often involves many conversations. A browser asks for resources; servers respond with content or an outcome.
A round trip behind the page
Simplified exchange after the connection is established.
- Browser → server
GET /catalog asks for the catalog.
- Server
Handles the request and chooses a response.
- Server → browser
200 OK with HTML; the browser displays it.
Read the visualA page loads but an image does not. Which explanation is plausible?
A document and its images can be fetched separately. Inspect the failed resource’s exchange instead of assuming the whole page failed.
Start with a resource
The browser may request an HTML document, then its style sheets, scripts, and images. A page can also request more data after it appears.
Separate both sides
Browser code runs on the visitor’s device. Server code handles requests on the service side. The browser interface can be changed by a visitor, so it cannot be the only place a security rule is enforced.
Follow the answer back
A response has a status and may include content. A successful document request does not promise that every later resource request will succeed.
Put it in context
The fictional Harbor Books catalog loads, but one cover image is missing. The catalog request can succeed while a separate image request fails. Inspecting each exchange helps locate the problem.
Make a decision.
Explore the practice space, then answer the check-in below. A correct answer lets you save this lesson to your progress.
YOUR PRACTICE SPACE
Try the idea for yourself.
Enable JavaScript to explore this fictional exercise. The explanation and visual above remain available.
Take this with you.
Follow each request and response separately. One page can depend on many exchanges.
Next lesson: Read URLs, headers, and status codes