ETag and conditional requests in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an ETag in HTTP?

An ETag (Entity Tag) is a unique identifier assigned by a server to a specific version of a resource. It helps browsers know if the resource has changed since the last time it was fetched.

beginner

How does a conditional request use an ETag?

A client sends the ETag it has in the 'If-None-Match' header. The server compares it with the current ETag. If they match, the server replies with 304 Not Modified, saving bandwidth by not sending the full resource again.

beginner

Which HTTP status code indicates the resource has not changed when using ETag conditional requests?

The status code 304 Not Modified means the resource has not changed and the client can use its cached version.

intermediate

In Node.js, which module is commonly used to handle ETag generation and conditional requests?

The 'http' module can be used directly, but frameworks like Express.js provide middleware (e.g., 'etag' middleware) to automatically generate and check ETags for responses.

beginner

Why are ETags useful for improving web performance?

ETags reduce unnecessary data transfer by letting clients know if their cached copy is still valid. This saves bandwidth and speeds up page loads by avoiding full downloads when content hasn't changed.

What header does a client send to perform a conditional request using an ETag?

A If-Match

B If-None-Match

C ETag

D Cache-Control

The client sends the 'If-None-Match' header with the ETag value to ask the server if the resource has changed.

What does the server respond with if the ETag matches the client's version?

A 304 Not Modified

B 500 Internal Server Error

C 404 Not Found

D 200 OK with full content

A 304 Not Modified response tells the client to use its cached version because the resource has not changed.

Which Node.js framework commonly helps manage ETags automatically?

A Express.js

B React

C Vue.js

D Angular

Express.js has built-in support and middleware to handle ETags and conditional requests.

What is the main benefit of using ETags in web applications?

A Speeds up server processing by caching requests

B Improves security by encrypting data

C Reduces bandwidth by avoiding sending unchanged data

D Allows multiple users to edit the same resource simultaneously

ETags help reduce bandwidth by letting clients reuse cached data when the resource hasn't changed.

If a client sends an ETag that does not match the server's current ETag, what happens?

A Server sends 304 Not Modified

B Server closes the connection

C Server sends 403 Forbidden

D Server sends 200 OK with updated resource

If the ETags don't match, the server sends the full updated resource with a 200 OK status.

Explain how ETags and conditional requests work together to optimize web resource loading.

Think about how your browser checks if a file has changed before downloading it again.

Describe how you would implement ETag support in a Node.js server using Express.

Express has built-in features to help with ETags and conditional requests.