Custom endpoint registration in Wordpress - Step-by-Step Execution

Concept Flow - Custom endpoint registration

Start WordPress Init

↓

Hook into 'rest_api_init'

↓

Call register_rest_route()

↓

Define endpoint path & methods

↓

Assign callback function

↓

Endpoint ready to handle requests

↓

Client sends request

↓

Callback runs, returns response

↓

Response sent back to client

WordPress hooks into initialization, registers a REST API endpoint with a path, methods, and callback, then handles requests by running the callback and returning the response.

Execution Sample

Wordpress

<?php
add_action('rest_api_init', function () {
  register_rest_route('myplugin/v1', '/data', [
    'methods' => 'GET',
    'callback' => 'myplugin_get_data',
  ]);
});

function myplugin_get_data() {
  return ['message' => 'Hello from custom endpoint'];
}

Registers a GET endpoint at /wp-json/myplugin/v1/data that returns a simple message.

Execution Table

Step	Action	Function Called	Parameters	Result
1	WordPress initializes REST API	add_action	'rest_api_init', callback	Callback registered for REST API init
2	REST API initializes	rest_api_init hook fires	none	Callback runs
3	Register endpoint	register_rest_route	'myplugin/v1', '/data', args	Endpoint registered at /myplugin/v1/data with GET method
4	Client sends GET request	N/A	GET /wp-json/myplugin/v1/data	Request received
5	Run callback	myplugin_get_data	none	Returns ['message' => 'Hello from custom endpoint']
6	Send response	N/A	Response JSON	Client receives JSON message
7	End	N/A	N/A	Request complete

💡 Request completes after callback returns response and client receives it

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
registered_endpoints	empty	contains /myplugin/v1/data GET endpoint	unchanged	unchanged
request	none	none	GET /wp-json/myplugin/v1/data	processed
response	none	none	['message' => 'Hello from custom endpoint']	sent to client

Key Moments - 2 Insights

Why do we hook into 'rest_api_init' instead of 'init' to register endpoints?

Because 'rest_api_init' runs specifically when the REST API is ready to register routes, ensuring endpoints are registered at the right time. See execution_table step 2 and 3.

What happens if the callback function is missing or returns nothing?

The endpoint will respond with an empty or error response, so the callback must return valid data. See execution_table step 5.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the endpoint actually registered?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check the 'Action' and 'Result' columns in step 3 for endpoint registration

According to variable_tracker, what is the state of 'response' after step 5?

A Empty

B Contains the callback return data

C Contains the client request

D Not defined yet

💡 Hint

Look at the 'response' row under 'After Step 5' column

If the client sends a POST request instead of GET, what happens based on the execution flow?

A Endpoint rejects request (method not allowed)

B Callback runs normally

C Endpoint registers a new POST route automatically

D WordPress crashes

💡 Hint

The registered endpoint only allows GET method as per step 3 parameters

Concept Snapshot

Custom endpoint registration in WordPress:
- Hook into 'rest_api_init'
- Use register_rest_route(namespace, route, args)
- Args include 'methods' and 'callback'
- Callback returns data for response
- Endpoint accessible at /wp-json/namespace/route
- Only registered methods accepted

Full Transcript

This visual execution trace shows how WordPress registers a custom REST API endpoint. First, WordPress hooks a function to 'rest_api_init' which runs when the REST API initializes. Inside this function, register_rest_route is called with a namespace, route path, and arguments including HTTP methods and a callback function. This registers the endpoint so WordPress knows to listen for requests at that URL. When a client sends a GET request to the endpoint, WordPress runs the callback function, which returns data. WordPress then sends this data back as a JSON response to the client. Variables like registered_endpoints, request, and response change state during these steps. Key moments include understanding why 'rest_api_init' is used and the importance of the callback returning data. The quiz tests knowledge of when registration happens, response content, and method restrictions.