const posthtml = require('posthtml')

const html = `<a>test1</a><span><a>test2</a></span><a>test1</a>`;
const plugins = [
  function(tree) {
    tree.walk(node => {
      if (node.tag === 'a' && (node.attrs === undefined || node.attrs.skip === undefined)) {
        node.attrs = {
          skip: true
        }

        return {
          tag: false,
          content: [
            {tag: 'a', content: 'test0', attrs: {skip: true}},
            node
          ]
        }
      }
      return node;
    });

    tree.match({tag: 'a'}, node => {
      delete node.attrs.skip;
      return node;
    })

    return tree;
  }
]
const options = {}

posthtml(plugins)
  .process(html, options)
  .then((result) =>  console.log(result.html))

// Or better use a plain object?
class Node {
  constructor(tag, attrs, content) {
    this.tag = tag;
    this.attrs = attrs;
    this.content = content;
  }
}

posthtml().use((tree) => {
  tree.match({ tag: 'p' }, (node) => {
    node.content ??= [
        new Node('span', { class: 'some' }, ['text']),
    ];

    return node;
  })
});