marked/test/helpers/html-differ.js

import { HtmlDiffer } from '@markedjs/html-differ';
const htmlDiffer = new HtmlDiffer({
  ignoreSelfClosingSlash: true,
  ignoreComments: false
});

export const isEqual = htmlDiffer.isEqual.bind(htmlDiffer);
export async function firstDiff(actual, expected, padding) {
  padding = padding || 30;
  const diffHtml = await htmlDiffer.diffHtml(actual, expected);
  const result = diffHtml.reduce((obj, diff) => {
    if (diff.added) {
      if (obj.firstIndex === null) {
        obj.firstIndex = obj.expected.length;
      }
      obj.expected += diff.value;
    } else if (diff.removed) {
      if (obj.firstIndex === null) {
        obj.firstIndex = obj.actual.length;
      }
      obj.actual += diff.value;
    } else {
      obj.actual += diff.value;
      obj.expected += diff.value;
    }

    return obj;
  }, {
    firstIndex: null,
    actual: '',
    expected: ''
  });

  return {
    actual: result.actual.substring(result.firstIndex - padding, result.firstIndex + padding),
    expected: result.expected.substring(result.firstIndex - padding, result.firstIndex + padding)
  };
}