Coding with an API
Coding with an APIMapping JS components to (Gutenberg) blocks

Mapping JS components to (Gutenberg) blocks

This guide presents an example Preact app that queries for block data and maps it into customized JavaScript components.

In order to run the Preact app below as a static .html file in the browser, the Schema Configuration applied to the endpoint needs to have Response Headers with the following value:

Access-Control-Allow-Origin: null
Access-Control-Allow-Headers: content-type,content-length,accept

(The HTML code below is inspired by the Preact example in Automattic/vip-block-data-api.)

The GraphQL query contained in the code below retrieves the post's block data as a JSON object (via field CustomPost.blockDataItems), and then the JavaScript code maps each block data item into a custom component:

<!DOCTYPE html>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Gato GraphQL - Mapping JS components to (Gutenberg) blocks: Preact example</title>
<script type="module">
  import { h, render } from '';
  // Input here your domain, and enable the single endpoint
  const endpoint = "";
  // Input here the ID of a post with blocks
  const postId = 40;
  renderPost(endpoint, postId);
  async function renderPost(endpoint, postId) {
    const data = {
      query: `
        query GetPost($postId: ID!) {
          post(by: { id: $postId }) {
      variables: {
        postId: `${ postId }`
    const response = await fetch(
        method: 'post',
        body: JSON.stringify(data),
        headers: {
          Accept: 'application/json',
          'Content-Type': 'application/json',
          'Content-Length': data.length,
    // Execute the query, and await the response
    const json = await response.json();
    // If the query produced errors, exit
    if (json.errors) {
    // Uncomment here to visualize the GraphQL response
    // console.log(;
    const postTitle =;
    const blocks =;
    const App = Post(postTitle, blocks);
    render(App, document.body);
  function mapBlockToComponent(block) {
    if ( === 'core/heading') {
      return Heading(block);
    } else if ( === 'core/paragraph') {
      return Paragraph(block);
    } else if ( === 'core/media-text') {
      return MediaText(block);
    } else if ( === 'core/gallery') {
      return Gallery(block);
    } else if ( === 'core/image') {
      return Image(block);
    } else {
      return null;
  /* Components */
  function Post(title, blocks) {
    return h('div', { className: 'post' },
      h('h1', null, title),,
  function Heading(props) {
    // Use dangerouslySetInnerHTML for rich text formatting
    return h('h2', { dangerouslySetInnerHTML: { __html: props.attributes.content } });
  function Paragraph(props) {
    // Use dangerouslySetInnerHTML for rich text formatting
    return h('p', { dangerouslySetInnerHTML: { __html: props.attributes.content } });
  function MediaText(props) {
    return h('div', { className: 'media-text' },
      h('div', { className: 'media' },
        h('img', { src: props.attributes.mediaUrl })
      h('div', { className: 'text' },
        props.innerBlocks ? : null,
  function Gallery(props) {
    return h('div', { className: 'gallery' },
      h('div', { className: 'images' },
        props.innerBlocks ? : null,
  function Image(props) {
    return h('img', { src: props.attributes.url });

Running the application produces the following HTML code from post data:

<div class="post">
  <h1>Welcome to a single post full of blocks!</h1>
  <p>When I look back on my past and think how much time I wasted on nothing, how much time has been lost in futilities, errors, laziness, incapacity to live; how little I appreciated it, how many times I sinned against my heart and soul-then my heart bleeds. <strong>Life is a gift, life is happiness, every minute can be an eternity of happiness</strong>. (<a href="" target="_blank" rel="noopener">Quote by Fyodor Dostoevsky</a>)<br></p>
  <h2>This blog post will be transformed...</h2>
  <p>If you make it a habit not to blame others, you will feel the growth of the ability to love in your soul, and you will see the growth of goodness in your life. (<a href="" target="_blank" rel="noopener">Quote by Leo Tolstoy</a>)<br></p>
  <img src="">
  <h2><mark style="background-color:#D1D1E4" class="has-inline-color">I love these veggies!!!</mark></h2>
  <h2>When going to eat out, I normally go for one of these:</h2>
  <h2>This heading (H3) is boring (Regex test: $1 #1), but these guys are not</h2>
  <div class="gallery">
    <div class="images">
      <img src="">
      <img src="">