WordPress RestAPI in Javascript. How to get array data out of the response

Question

I am working on a Gutenberg block and am modifying the Edit.js file. I want to fetch the root categories in the database. From the reading I have done, it seems a good way to do this is to use the REST API and perform a call like this:

var categories = fetch("http://localhost/wordpress_ttm/wp-json/wp/v2/categories")
                .then(response => response.json())

This all works fine and gives me back a response. Here is the structure of the response.

categories: Promise { "fulfilled" }
<state>: "fulfilled"
<value>: (10) […]
0: {…}
1: {…}
2: {…}
3: {…}
4: {…}
5: {…}
6: {…}
7: {…}
8: {…}
9: {…}
length: 10
<prototype>: []
<prototype>: Promise.prototype

How do I to get the data out of the response? I want to grab the array data and iterate over it, but I'm not sure how to do that.

Martin Lévai · Accepted Answer · 2025-10-12 19:37:59Z

1

fetch() is asynchronous so it returns a Promise -> you can’t access the data directly right after calling fetch(). In other words, you need to use .then() multiple times like this (this is called chaining):

fetch("http://localhost/wordpress_ttm/wp-json/wp/v2/categories")
  .then((response) => response.json()) // parse JSON
  .then((categories) => {
    console.log(categories); // now you can work with the array

    // Example loop
    categories.forEach((category) => {
      console.log(category.name);
    });
  })
  .catch((error) => {
    console.error("Error fetching categories:", error);
  });

answered Oct 12 at 19:37

Martin Lévai

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