WP Rest API: details of latest post including featured media url in one request?

I’m using wp-rest api to get posts information.
I also use wp rest api filter items to filter fields and summarize the result:

When I call http://example.com/wp-json/wp/v2/posts?items=id,title,featured_media it returns results like this:

[

    {
        "id": 407,
        "title": {
            "rendered": "Title 1"
        },
        "featured_media": 399
    },
    {
        "id": 403,
        "title": {
            "rendered": "Title 2"
        },
        "featured_media": 401
    }

]

The question is how can I generate featured media url using this id? By default calling http://example.com/wp-json/wp/v2/media/401 returns a new json which have all details about url of different sizes of source image:

{

    "id": 401,
    "date": "2016-06-03T17:29:09",
    "date_gmt": "2016-06-03T17:29:09",
    "guid": {
        "rendered": "http://example.com/wp-content/uploads/my-image-name.png"
    },
    "modified": "2016-06-03T17:29:09",
    "modified_gmt": "2016-06-03T17:29:09",
    "slug": "my-image-name",
    "type": "attachment",
    "link": "http://example.com/my-post-url",
    "title": {
        "rendered": "my-image-name"
    },
    "author": 1,
    "comment_status": "open",
    "ping_status": "closed",
    "alt_text": "",
    "caption": "",
    "description": "",
    "media_type": "image",
    "mime_type": "image/png",
    "media_details": {
        "width": 550,
        "height": 250,
        "file": "my-image-name.png",
        "sizes": {
            "thumbnail": {
                "file": "my-image-name-150x150.png",
                "width": 150,
                "height": 150,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-150x150.png"
            },
            "medium": {
                "file": "my-image-name-300x136.png",
                "width": 300,
                "height": 136,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-300x136.png"
            },
            "one-paze-port-thumb": {
                "file": "my-image-name-363x250.png",
                "width": 363,
                "height": 250,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-363x250.png"
            },
            "one-paze-blog-thumb": {
                "file": "my-image-name-270x127.png",
                "width": 270,
                "height": 127,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-270x127.png"
            },
            "one-paze-team-thumb": {
                "file": "my-image-name-175x175.png",
                "width": 175,
                "height": 175,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-175x175.png"
            },
            "one-paze-testimonial-thumb": {
                "file": "my-image-name-79x79.png",
                "width": 79,
                "height": 79,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-79x79.png"
            },
            "one-paze-blog-medium-image": {
                "file": "my-image-name-380x250.png",
                "width": 380,
                "height": 250,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name-380x250.png"
            },
            "full": {
                "file": "my-image-name.png",
                "width": 550,
                "height": 250,
                "mime_type": "image/png",
                "source_url": "http://example.com/wp-content/uploads/my-image-name.png"
            }
        },
        "image_meta": {
            "aperture": "0",
            "credit": "",
            "camera": "",
            "caption": "",
            "created_timestamp": "0",
            "copyright": "",
            "focal_length": "0",
            "iso": "0",
            "shutter_speed": "0",
            "title": "",
            "orientation": "0",
            "keywords": [ ]
        }
    },
    "post": 284,
    "source_url": "http://example.com/wp-content/uploads/my-image-name.png",
    "_links": {
        "self": [
            {
                "href": "http://example.com/wp-json/wp/v2/media/401"
            }
        ],
        "collection": [
            {
                "href": "http://example.com/wp-json/wp/v2/media"
            }
        ],
        "about": [
            {
                "href": "http://example.com/wp-json/wp/v2/types/attachment"
            }
        ],
        "author": [
            {
                "embeddable": true,
                "href": "http://example.com/wp-json/wp/v2/users/1"
            }
        ],
        "replies": [
            {
                "embeddable": true,
                "href": "http://example.com/wp-json/wp/v2/comments?post=401"
            }
        ]
    }

}

But consider the case when I want to get list of posts and their thumbnails. One time I should call http://example.com/wp-json/wp/v2/posts?items=id,title,featured_media then I should call http://example.com/wp-json/wp/v2/media/id 10 times for each media id and then parse the results and get final url of media thumbnail. So it needs 11 request for get details of 10 post (one for list,10 for thumbnails).
Is it possible to get this results in one request?

Ah I just had this problem myself! And while _embed is great, in my experience it is very slow, and the point of JSON is to be fast 😀

I have the following code in a plugin (used for adding custom post types), but I imagine you could put it in your theme’s function.php file.

php

add_action( 'rest_api_init', 'add_thumbnail_to_JSON' );
function add_thumbnail_to_JSON() {
//Add featured image
register_rest_field( 
    'post', // Where to add the field (Here, blog posts. Could be an array)
    'featured_image_src', // Name of new field (You can call this anything)
    array(
        'get_callback'    => 'get_image_src',
        'update_callback' => null,
        'schema'          => null,
         )
    );
}

function get_image_src( $object, $field_name, $request ) {
  $feat_img_array = wp_get_attachment_image_src(
    $object['featured_media'], // Image attachment ID
    'thumbnail',  // Size.  Ex. "thumbnail", "large", "full", etc..
    true // Whether the image should be treated as an icon.
  );
  return $feat_img_array[0];
}

Now in your JSON response you should see a new field called "featured_image_src": containing a url to the thumbnail.

Read more about modifying responses here:
http://v2.wp-api.org/extending/modifying/

And here’s more information on theregister_rest_field and wp_get_attachment_image_src() functions:
1.) https://developer.wordpress.org/reference/functions/register_rest_field/
2.) https://developer.wordpress.org/reference/functions/wp_get_attachment_image_src/

**Note: Don’t forget <?php ?> tags if this is a new php file!