marked/src/Slugger.js

/**
 * Slugger generates header id
 */
module.exports = class Slugger {
  constructor() {
    this.seen = {};
  }

  /**
   * Convert string to unique id
   */
  slug(value) {
    let slug = value
      .toLowerCase()
      .trim()
      // remove html tags
      .replace(/<[!\/a-z].*?>/ig, '')
      // remove unwanted chars
      .replace(/[\u2000-\u206F\u2E00-\u2E7F\\'!"#$%&()*+,./:;<=>?@[\]^`{|}~]/g, '')
      .replace(/\s/g, '-');

    if (this.seen.hasOwnProperty(slug)) {
      const originalSlug = slug;
      do {
        this.seen[originalSlug]++;
        slug = originalSlug + '-' + this.seen[originalSlug];
      } while (this.seen.hasOwnProperty(slug));
    }
    this.seen[slug] = 0;

    return slug;
  }
};