Implement a function generateTOC(root) that constructs a Table of Contents (TOC) from an HTML document.

The function should:

• Accept a root element to search within.
• Identify heading elements (<h1> to <h6>) in the order they appear.
• Return an array of objects with level (heading level) and text (heading content).

Examples

const doc = new DOMParser().parseFromString(`
  <div>
    <h1>Introduction</h1>
    <h2>Background</h2>
    <h2>Goals</h2>
    <h1>Conclusion</h1>
  </div>`, 'text/html');

generateTOC(doc.body);
// [
//   { level: 1, text: 'Introduction' },
//   { level: 2, text: 'Background' },
//   { level: 2, text: 'Goals' },
//   { level: 1, text: 'Conclusion' }
// ]