Martin Pettersson

An extension for the WP REST API that exposes endpoints for sidebars and widgets.
note: this plugin is under heavy development and will receive frequent feature updates (including documentation) so stay tuned and checkout the <a href="https://github.com/martin-pettersson/wp-rest-api-sidebars" rel="nofollow ugc">github</a> repo for the latest updates
<h4>Currently supported endpoints</h4>

/wp-json/wp-rest-api-sidebars/v1/sidebars returns a list of registered sidebars
<pre><code>[
 {
 "name": "Sidebar Name",
 "id": "sidebar-id",
 "description": "Sidebar description...",
 "class": "sidebar-class",
 "before_widget": "<aside id=\"%1$s\" class=\"widget %2$s\">",
 "after_widget": "<\/aside>",
 "before_title": "<h1 class=\"widget-title\">",
 "after_title": "<\/h1>"
 }
]
</code></pre>
/wp-json/wp-rest-api-sidebars/v1/sidebars/{id} returns the given sidebar
<pre><code>{
 "name": "Sidebar Name",
 "id": "sidebar-id",
 "description": "Sidebar description...",
 "class": "sidebar-class",
 "before_widget": "<aside id=\"%1$s\" class=\"widget %2$s\">",
 "after_widget": "<\/aside>",
 "before_title": "<h1 class=\"widget-title\">",
 "after_title": "<\/h1>",
 "rendered": "<aside id=\"widget-id-1\" class=\"widget widget_widget-id\">...",
 "widgets": [
 {
 "name": "Widget Name",
 "id": "widget-name-1",
 "classname": "widget_widget_name",
 "description": "Widget description",
 "rendered": "<aside id=\"widget-names-1\" class=\"widget widget_widget_name\">..."
 }
 ]
}
</code></pre>

WP REST API Sidebars

Works great!

An extension for the WP REST API that exposes endpoints for sidebars and widgets.

svrooij

Since wordpress version 4.9.? wordpress includes the functionality provided by this plugin in the core of wordpress.
Checkout https://developer.wordpress.org/rest-api/using-the-rest-api/global-parameters/#_fields for functionality included in the wordpress core, 
they made it even better by filtering the amount of data pulled from the database.
This plugin will no longer be maintained since it has been superseded by the core functionality.
The <a href="https://wordpress.org/plugins/rest-api/" rel="ugc">wp-rest-api-v2</a> returns a lot of properties. 
It could be very useful (or mobile-data-friendly) to only return the properties needed by the application.
If you only want titles and links of some articles it doesn’t make sense to return the content or the excerpt.
This isn’t limited to posts, it also works on custom posttypes, categories, pages, terms, taxonomies and comments.
Instead of returning:
<pre><code>{
 "id": 2138,
 "date": "2015-10-25T15:31:03",
 "guid": {
 "rendered": "http://worldofict.nl/?p=2138"
 },
 "modified": "2015-10-25T15:31:03",
 "modified_gmt": "2015-10-25T14:31:03",
 "slug": "rechtenvrije-fotos",
 "type": "post",
 "link": "http://worldofict.nl/tip/2138-rechtenvrije-fotos/",
 "title": {
 "rendered": "Rechtenvrije foto’s"
 },
 "content": {
 "rendered": ".. A lot of content .. "
 },
 "excerpt": {
 "rendered": " .. A lot of content ..."
 },
 "author": 2,
 "featured_image": 2139,
 "comment_status": "open",
 "ping_status": "open",
 "sticky": false,
 "format": "standard",
 //.. even more tags ....
}
</code></pre>
It can return (with <code>fields=id,title.rendered,link</code> as GET parameter)
<pre><code>{
 "id": 2138,
 "link": "http://worldofict.nl/tip/2138-rechtenvrije-fotos/",
 "title": {
 "rendered": "Rechtenvrije foto’s"
 }
}
</code></pre>
<h4>Notes</h4>
<ol>
<li>If you specify fields so it wouldn’t return data the default response is send back to the client.</li>
<li>(for developers) something wrong with this plugin? <a href="https://github.com/svrooij/rest-api-filter-fields/" rel="nofollow ugc">Github</a></li>
<li>If you liked the plugin <a href="https://github.com/sponsors/svrooij" rel="nofollow ugc">consider sponsoring me</a></li>
</ol>

REST API – Filter Fields

This is hands-down the best REST API extension available.

Best REST API plugin

Filter the properties returned by the Wordpress rest api V2 (only needed until wordpress 4.9)

WP REST API Sidebars vs REST API – Filter Fields