WP API featured image attachment

I have found an answer https:\\wordpress.stackexchange.com/questions/241271/wp-rest-api-details-of-latest-post-including-featured-media-url-in-one-request I added this code to my functions file in the GET request location

add_action( 'rest_api_init', 'add_thumbnail_to_JSON' );
function add_thumbnail_to_JSON() {
//Add featured image
register_rest_field('post',
    'featured_image_src', //NAME OF THE NEW FIELD TO BE ADDED - 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'], 'thumbnail', true);
return $feat_img_array[0];
}
then called ourHTMLString += '<img src=' + postsData[i].featured_image_src + '>';

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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 :D

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: