res.set for response headers in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does res.set() do in Express?

res.set() sets HTTP response headers before sending the response to the client.

beginner

How do you set multiple headers at once using res.set()?

You pass an object with key-value pairs where keys are header names and values are header values.

res.set({ 'Content-Type': 'application/json', 'Cache-Control': 'no-cache' })

intermediate

Can you overwrite an existing header using res.set()?

Yes, calling res.set() with the same header name will overwrite the previous value.

intermediate

What is the difference between res.set() and res.header() in Express?

They are aliases and behave the same way. Both set response headers.

beginner

Why is setting response headers important in web development?

Headers control how browsers and clients handle the response, like content type, caching, security, and more.

How do you set a single response header using res.set()?

A res.set('text/html')

B res.set({'Content-Type'})

C res.set('Content-Type')

D res.set('Content-Type', 'text/html')

Use res.set(headerName, value) to set a single header.

What happens if you call res.set() twice with the same header name?

A The header value is overwritten with the last call

B Both values are sent as a list

C An error is thrown

D The first value is kept, the second ignored

Calling res.set() again with the same header name overwrites the previous value.

Which of these is a valid way to set multiple headers at once?

A res.set('X-Test', '123', 'X-Flag', 'true')

B res.set({ 'X-Test': '123', 'X-Flag': 'true' })

C res.set(['X-Test', '123'], ['X-Flag', 'true'])

D res.set('X-Test:X-Flag', '123:true')

Passing an object with header names and values sets multiple headers at once.

Is res.header() different from res.set() in Express?

A Yes, <code>res.set()</code> only sets cookies

B Yes, <code>res.header()</code> only reads headers

C No, they are aliases and work the same

D Yes, <code>res.header()</code> is deprecated

Both methods do the same thing: set response headers.

Why might you set the Cache-Control header using res.set()?

A To control how browsers cache the response

B To set the page title

C To change the HTTP method

D To redirect the user

Cache-Control tells browsers how to store or not store the response.

Explain how to use res.set() to add headers to an Express response. Include examples for single and multiple headers.

Think about how you tell the browser what type of content you are sending or how to cache it.

Why is setting response headers important in web applications? Give at least two reasons.

Consider what happens if the browser does not know what kind of data it received.