const { SiteClient } = require('datocms-client');
async function run() {
  const client = new SiteClient('YOUR-API-TOKEN');
  
  const modelIdOrApiKey = 'blog_post';
  const fieldset = await client.fieldset.create(modelIdOrApiKey, {
    title: 'SEO-related fields',
    hint: 'Please fill in these fields!',
    position: 1,
    collapsible: true,
    startCollapsed: false
  });
  
  console.log(fieldset);
}
run();

> node example.js
{
  "id": "124",
  "title": "SEO-related fields",
  "hint": "Please fill in these fields!",
  "collapsible": true,
  "startCollapsed": false,
  "position": 1,
  "itemType": "44"
}