marked/test/helpers/html-differ.js

const HtmlDiffer = require('@markedjs/html-differ').HtmlDiffer;
const htmlDiffer = new HtmlDiffer({ ignoreSelfClosingSlash: true });

module.exports = {
  isEqual: htmlDiffer.isEqual.bind(htmlDiffer),
  firstDiff: (actual, expected, padding) => {
    padding = padding || 30;
    const result = htmlDiffer
      .diffHtml(actual, expected)
      .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)
    };
  }
};