HTTP method handlers (GET, POST) in NextJS - Step-by-Step Execution

Concept Flow - HTTP method handlers (GET, POST)

Request arrives

↓

Check HTTP method

↓

Run GET handler

↓

Send GET response

↓

Request ends

When a request comes in, Next.js checks its HTTP method. It runs the matching handler (GET or POST) and sends back the response.

Execution Sample

NextJS

export async function GET(request) {
  return new Response('Hello GET');
}

export async function POST(request) {
  return new Response('Hello POST');
}

This code defines two handlers: one for GET requests and one for POST requests, each sending a simple text response.

Execution Table

Step	Incoming Request Method	Handler Chosen	Action	Response Sent
1	GET	GET handler	Run GET function	'Hello GET'
2	POST	POST handler	Run POST function	'Hello POST'
3	PUT	No handler	No matching function	405 Method Not Allowed
4	DELETE	No handler	No matching function	405 Method Not Allowed

💡 Execution stops after sending response or if no handler matches the HTTP method.

Variable Tracker

Variable	Start	After GET Request	After POST Request	After PUT Request
request.method	undefined	GET	POST	PUT
handler chosen	none	GET handler	POST handler	none
response	none	'Hello GET'	'Hello POST'	405 Method Not Allowed

Key Moments - 3 Insights

Why does a PUT request get no response from these handlers?

Because the code only defines GET and POST handlers. PUT requests have no matching function, so Next.js returns a 405 Method Not Allowed response as shown in execution_table row 3.

Can both GET and POST handlers run for the same request?

No. Only the handler matching the request's HTTP method runs. For example, a GET request runs only the GET handler (execution_table row 1).

What happens if the POST handler takes time to respond?

The POST handler is async, so Next.js waits for it to finish before sending the response. This is shown by the async function in the execution_sample.

Visual Quiz - 3 Questions

Look at the execution_table. What response is sent when the request method is POST?

A 'Hello POST'

B 'Hello GET'

C 405 Method Not Allowed

D No response

💡 Hint

Check execution_table row 2 under 'Response Sent'

At which step does the handler chosen become 'none' due to no matching function?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at execution_table rows 3 and 4 for 'Handler Chosen'

If you add a PUT handler, how would the response for a PUT request change in the variable_tracker?

A handler chosen would stay 'none'

B request.method would change from 'PUT' to 'POST'

C response would change from '405 Method Not Allowed' to the PUT handler's response

D response would stay 'Hello GET'

💡 Hint

See variable_tracker row 'response' for PUT request and imagine adding a PUT handler

Concept Snapshot

Next.js API routes use exported async functions named after HTTP methods.
Define GET(request) for GET requests and POST(request) for POST requests.
Next.js calls the matching handler based on request.method.
If no handler matches, Next.js returns 405 Method Not Allowed by default.
Handlers return Response objects to send back data.
This pattern keeps server code clear and organized.

Full Transcript

In Next.js, when a request arrives, the framework looks at the HTTP method like GET or POST. It then runs the matching exported async function named GET or POST. For example, if the request method is GET, Next.js runs the GET handler function and sends its response. If the method is POST, it runs the POST handler. If there is no handler for the method, Next.js returns a 405 Method Not Allowed response. This way, you can organize your server code by HTTP method. Each handler receives the request object and returns a Response. This example shows simple handlers returning text responses for GET and POST. The execution table traces how requests with different methods choose handlers and what responses are sent. The variable tracker shows how request.method, handler chosen, and response change step by step. Key moments clarify why some methods get no response and how async handlers work. The quiz tests understanding of which handler runs and what response is sent. This pattern helps keep server logic clear and easy to maintain.