lol-html

The lol-html JavaScript API provides an HTMLRewriter class for streaming HTML rewriter functionality. You can use it to intercept elements, modify attributes, and react to tag lifecycle events (like onEndTag) while processing HTML chunks.

To use it, instantiate HTMLRewriter with a character encoding and a callback function that handles output chunks. Use .on(selector, handlers) to define transformations for specific elements, and .write(buffer) to feed HTML data into the rewriter. Finally, call .end() to signal the end of the stream.

'use strict';

const { HTMLRewriter } = require('lol-html'); // path/to/lol-html.js

const chunks = [];
const rewriter = new HTMLRewriter('utf8', (chunk) => {
  chunks.push(chunk);
});

rewriter.on('a[href]', {
  element(el) {
    const href = el
      .getAttribute('href')
      .replace('http:', 'https:');
    el.setAttribute('href', href);

    el.onEndTag((tag)=> {
      console.log(`Tag ended: ${tag.name}`);
    });
  },
});

[
  '<div><a href=',
  'http://example.com>',
  '</a></div>',
].forEach((part) => {
  rewriter.write(Buffer.from(part));
});

rewriter.end();

const output = Buffer.concat(chunks).toString('utf8');
console.log(output);

The C API provides functions for mutating HTML content and handling streaming output.

Content Mutation

Functions for content mutation (e.g., inserting text or elements) require:

• A valid, non-NULL pointer to the mutation handler.
• content: A valid UTF-8 string.
• content_len: The length of the content.
• is_html: A boolean indicating if the content should be treated as HTML (written without escaping) or plain text.

Returns 0 on success, or a non-zero error code on failure.

Streaming

Streaming operations use the CStreamingHandler to provide callbacks for writing content.

• The CStreamingHandler must be valid and non-NULL.
• The streaming_writer is copied immediately and is not guaranteed a stable address.
• The streaming_writer can be used from another thread (Send) but is not thread-safe for concurrent access (!Sync).

Returns 0 on success, or -1 if the handler is invalid or the writer is NULL.