The method within core.php of the JSON API plugin for Wordpress. The core.php file is located within "json-api/controllers"

core.php

public function get_recent_summary() {
    global $json_api;
    $posts = $json_api->introspector->get_posts();
    $output = array();
    
    foreach ($posts as $post){
      $post_summary["id"] = $post->id;
    	$post_summary["url"] = $post->url;
    	$post_summary["title"] = $post->title;
    	$post_summary["date"] = $post->date;
    	$post_summary["author"] = $post->author->name;
    	$post_summary["thumbnail"] = $post->attachments[0]->images["thumbnail"]->url;
    	$output[] = $post_summary;
    	
    }
            
    return $this->posts_result($output);
  }