WordPress REST API Custom Endpoint Example

wp_rest_api_endpoint_example.php

<?php  
/* 1. add function to rest_api_init hook, */
/* 2. then, call register_rest_route() function */
add_action( 'rest_api_init', 'define_endpoint');
function define_endpoint(){
	register_rest_route( 'namespace', '/new/route', array(
				'methods'         => array('POST','GET','UPDATE','DELETE'),
				'callback'        => 'my_awesome_func'
			) );
}
/* 2.a my_awesome_func() callback function */
function my_awesome_func( WP_REST_Request $request ) {
    // You can access parameters via direct array access on the object:
    $param = $request['some_param'];

    // Or via the helper method:
    $param = $request->get_param( 'some_param' );

    // You can get the combined, merged set of parameters:
    $parameters = $request->get_params();

    // The individual sets of parameters are also available, if needed:
    $parameters = $request->get_url_params();
    $parameters = $request->get_query_params();
    $parameters = $request->get_body_params();
    $parameters = $request->get_default_params();

    // Uploads aren't merged in, but can be accessed separately:
    $parameters = $request->get_file_params();
}
?>