Conditional requests handling in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of conditional requests in Express?

Conditional requests help the server decide if it needs to send the full response or just a status like 304 Not Modified, saving bandwidth and improving speed.

beginner

Which HTTP headers are commonly used for conditional requests?

The main headers are If-None-Match (for ETag) and If-Modified-Since (for last modified date). They tell the server what version the client has.

intermediate

How does Express help handle conditional GET requests?

Express provides the res.sendFile() and res.send() methods that automatically check request headers and send a 304 status if the resource is unchanged.

intermediate

What is an ETag and how is it used in Express conditional requests?

An ETag is a unique identifier for a resource version. Express can set ETags automatically, and clients send them back in If-None-Match headers to check if the resource changed.

advanced

How can you manually handle conditional requests in Express?

You can check request headers like req.headers['if-none-match'] or req.headers['if-modified-since'], compare with your resource state, and respond with res.status(304).end() if unchanged.

Which status code indicates the resource has NOT changed in a conditional request?

A 200 OK

B 500 Internal Server Error

C 404 Not Found

D 304 Not Modified

304 Not Modified tells the client the cached resource is still valid, so no new data is sent.

Which header does the client send to check if the resource's ETag matches?

A If-None-Match

B If-Modified-Since

C ETag

D Content-Type

If-None-Match carries the ETag value from the client to check if the resource changed.

What does Express do when you use res.sendFile() with conditional headers?

A Always sends full file content

B Automatically sends 304 if resource is unchanged

C Ignores conditional headers

D Throws an error

Express checks conditional headers and sends 304 Not Modified if the file hasn't changed.

Which header is used to check if a resource has been modified since a certain date?

A Last-Modified

B If-None-Match

C If-Modified-Since

D Content-Length

If-Modified-Since lets the client ask if the resource changed after a specific date.

How can you respond with 304 Not Modified manually in Express?

A res.status(304).end()

B res.send(304)

C res.json(304)

D res.redirect(304)

Use res.status(304).end() to send a 304 status with no body.

Explain how Express handles conditional GET requests using ETag and If-None-Match headers.

Think about how the server knows if the client has the latest version.

Describe how you would manually implement conditional request handling in an Express route.

Focus on checking headers and deciding the response status.