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https://www.communecter.org/plugins/turndown/turndown.js?v=1790224428379

js communecter.org collected 2026-09-24 09:22:52 UTC 26,759 bytes, 974 lines download raw bytes

1var TurndownService = (function () {
2  'use strict';
3
4  function extend (destination) {
5    for (var i = 1; i < arguments.length; i++) {
6      var source = arguments[i];
7      for (var key in source) {
8        if (source.hasOwnProperty(key)) destination[key] = source[key];
9      }
10    }
11    return destination
12  }
13
14  function repeat (character, count) {
15    return Array(count + 1).join(character)
16  }
17
18  function trimLeadingNewlines (string) {
19    return string.replace(/^\n*/, '')
20  }
21
22  function trimTrailingNewlines (string) {
23    // avoid match-at-end regexp bottleneck, see #370
24    var indexEnd = string.length;
25    while (indexEnd > 0 && string[indexEnd - 1] === '\n') indexEnd--;
26    return string.substring(0, indexEnd)
27  }
28
29  var blockElements = [
30    'ADDRESS', 'ARTICLE', 'ASIDE', 'AUDIO', 'BLOCKQUOTE', 'BODY', 'CANVAS',
31    'CENTER', 'DD', 'DIR', 'DIV', 'DL', 'DT', 'FIELDSET', 'FIGCAPTION', 'FIGURE',
32    'FOOTER', 'FORM', 'FRAMESET', 'H1', 'H2', 'H3', 'H4', 'H5', 'H6', 'HEADER',
33    'HGROUP', 'HR', 'HTML', 'ISINDEX', 'LI', 'MAIN', 'MENU', 'NAV', 'NOFRAMES',
34    'NOSCRIPT', 'OL', 'OUTPUT', 'P', 'PRE', 'SECTION', 'TABLE', 'TBODY', 'TD',
35    'TFOOT', 'TH', 'THEAD', 'TR', 'UL'
36  ];
37
38  function isBlock (node) {
39    return is(node, blockElements)
40  }
41
42  var voidElements = [
43    'AREA', 'BASE', 'BR', 'COL', 'COMMAND', 'EMBED', 'HR', 'IMG', 'INPUT',
44    'KEYGEN', 'LINK', 'META', 'PARAM', 'SOURCE', 'TRACK', 'WBR'
45  ];
46
47  function isVoid (node) {
48    return is(node, voidElements)
49  }
50
51  function hasVoid (node) {
52    return has(node, voidElements)
53  }
54
55  var meaningfulWhenBlankElements = [
56    'A', 'TABLE', 'THEAD', 'TBODY', 'TFOOT', 'TH', 'TD', 'IFRAME', 'SCRIPT',
57    'AUDIO', 'VIDEO'
58  ];
59
60  function isMeaningfulWhenBlank (node) {
61    return is(node, meaningfulWhenBlankElements)
62  }
63
64  function hasMeaningfulWhenBlank (node) {
65    return has(node, meaningfulWhenBlankElements)
66  }
67
68  function is (node, tagNames) {
69    return tagNames.indexOf(node.nodeName) >= 0
70  }
71
72  function has (node, tagNames) {
73    return (
74      node.getElementsByTagName &&
75      tagNames.some(function (tagName) {
76        return node.getElementsByTagName(tagName).length
77      })
78    )
79  }
80
81  var rules = {};
82
83  rules.paragraph = {
84    filter: 'p',
85
86    replacement: function (content) {
87      return '\n\n' + content + '\n\n'
88    }
89  };
90
91  rules.lineBreak = {
92    filter: 'br',
93
94    replacement: function (content, node, options) {
95      return options.br + '\n'
96    }
97  };
98
99  rules.heading = {
100    filter: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'],
101
102    replacement: function (content, node, options) {
103      var hLevel = Number(node.nodeName.charAt(1));
104
105      if (options.headingStyle === 'setext' && hLevel < 3) {
106        var underline = repeat((hLevel === 1 ? '=' : '-'), content.length);
107        return (
108          '\n\n' + content + '\n' + underline + '\n\n'
109        )
110      } else {
111        return '\n\n' + repeat('#', hLevel) + ' ' + content + '\n\n'
112      }
113    }
114  };
115
116  rules.blockquote = {
117    filter: 'blockquote',
118
119    replacement: function (content) {
120      content = content.replace(/^\n+|\n+$/g, '');
121      content = content.replace(/^/gm, '> ');
122      return '\n\n' + content + '\n\n'
123    }
124  };
125
126  rules.list = {
127    filter: ['ul', 'ol'],
128
129    replacement: function (content, node) {
130      var parent = node.parentNode;
131      if (parent.nodeName === 'LI' && parent.lastElementChild === node) {
132        return '\n' + content
133      } else {
134        return '\n\n' + content + '\n\n'
135      }
136    }
137  };
138
139  rules.listItem = {
140    filter: 'li',
141
142    replacement: function (content, node, options) {
143      content = content
144        .replace(/^\n+/, '') // remove leading newlines
145        .replace(/\n+$/, '\n') // replace trailing newlines with just a single one
146        .replace(/\n/gm, '\n    '); // indent
147      var prefix = options.bulletListMarker + '   ';
148      var parent = node.parentNode;
149      if (parent.nodeName === 'OL') {
150        var start = parent.getAttribute('start');
151        var index = Array.prototype.indexOf.call(parent.children, node);
152        prefix = (start ? Number(start) + index : index + 1) + '.  ';
153      }
154      return (
155        prefix + content + (node.nextSibling && !/\n$/.test(content) ? '\n' : '')
156      )
157    }
158  };
159
160  rules.indentedCodeBlock = {
161    filter: function (node, options) {
162      return (
163        options.codeBlockStyle === 'indented' &&
164        node.nodeName === 'PRE' &&
165        node.firstChild &&
166        node.firstChild.nodeName === 'CODE'
167      )
168    },
169
170    replacement: function (content, node, options) {
171      return (
172        '\n\n    ' +
173        node.firstChild.textContent.replace(/\n/g, '\n    ') +
174        '\n\n'
175      )
176    }
177  };
178
179  rules.fencedCodeBlock = {
180    filter: function (node, options) {
181      return (
182        options.codeBlockStyle === 'fenced' &&
183        node.nodeName === 'PRE' &&
184        node.firstChild &&
185        node.firstChild.nodeName === 'CODE'
186      )
187    },
188
189    replacement: function (content, node, options) {
190      var className = node.firstChild.getAttribute('class') || '';
191      var language = (className.match(/language-(\S+)/) || [null, ''])[1];
192      var code = node.firstChild.textContent;
193
194      var fenceChar = options.fence.charAt(0);
195      var fenceSize = 3;
196      var fenceInCodeRegex = new RegExp('^' + fenceChar + '{3,}', 'gm');
197
198      var match;
199      while ((match = fenceInCodeRegex.exec(code))) {
200        if (match[0].length >= fenceSize) {
201          fenceSize = match[0].length + 1;
202        }
203      }
204
205      var fence = repeat(fenceChar, fenceSize);
206
207      return (
208        '\n\n' + fence + language + '\n' +
209        code.replace(/\n$/, '') +
210        '\n' + fence + '\n\n'
211      )
212    }
213  };
214
215  rules.horizontalRule = {
216    filter: 'hr',
217
218    replacement: function (content, node, options) {
219      return '\n\n' + options.hr + '\n\n'
220    }
221  };
222
223  rules.inlineLink = {
224    filter: function (node, options) {
225      return (
226        options.linkStyle === 'inlined' &&
227        node.nodeName === 'A' &&
228        node.getAttribute('href')
229      )
230    },
231
232    replacement: function (content, node) {
233      var href = node.getAttribute('href');
234      if (href) href = href.replace(/([()])/g, '\\$1');
235      var title = cleanAttribute(node.getAttribute('title'));
236      if (title) title = ' "' + title.replace(/"/g, '\\"') + '"';
237      return '[' + content + '](' + href + title + ')'
238    }
239  };
240
241  rules.referenceLink = {
242    filter: function (node, options) {
243      return (
244        options.linkStyle === 'referenced' &&
245        node.nodeName === 'A' &&
246        node.getAttribute('href')
247      )
248    },
249
250    replacement: function (content, node, options) {
251      var href = node.getAttribute('href');
252      var title = cleanAttribute(node.getAttribute('title'));
253      if (title) title = ' "' + title + '"';
254      var replacement;
255      var reference;
256
257      switch (options.linkReferenceStyle) {
258        case 'collapsed':
259          replacement = '[' + content + '][]';
260          reference = '[' + content + ']: ' + href + title;
261          break
262        case 'shortcut':
263          replacement = '[' + content + ']';
264          reference = '[' + content + ']: ' + href + title;
265          break
266        default:
267          var id = this.references.length + 1;
268          replacement = '[' + content + '][' + id + ']';
269          reference = '[' + id + ']: ' + href + title;
270      }
271
272      this.references.push(reference);
273      return replacement
274    },
275
276    references: [],
277
278    append: function (options) {
279      var references = '';
280      if (this.references.length) {
281        references = '\n\n' + this.references.join('\n') + '\n\n';
282        this.references = []; // Reset references
283      }
284      return references
285    }
286  };
287
288  rules.emphasis = {
289    filter: ['em', 'i'],
290
291    replacement: function (content, node, options) {
292      if (!content.trim()) return ''
293      return options.emDelimiter + content + options.emDelimiter
294    }
295  };
296
297  rules.strong = {
298    filter: ['strong', 'b'],
299
300    replacement: function (content, node, options) {
301      if (!content.trim()) return ''
302      return options.strongDelimiter + content + options.strongDelimiter
303    }
304  };
305
306  rules.code = {
307    filter: function (node) {
308      var hasSiblings = node.previousSibling || node.nextSibling;
309      var isCodeBlock = node.parentNode.nodeName === 'PRE' && !hasSiblings;
310
311      return node.nodeName === 'CODE' && !isCodeBlock
312    },
313
314    replacement: function (content) {
315      if (!content) return ''
316      content = content.replace(/\r?\n|\r/g, ' ');
317
318      var extraSpace = /^`|^ .*?[^ ].* $|`$/.test(content) ? ' ' : '';
319      var delimiter = '`';
320      var matches = content.match(/`+/gm) || [];
321      while (matches.indexOf(delimiter) !== -1) delimiter = delimiter + '`';
322
323      return delimiter + extraSpace + content + extraSpace + delimiter
324    }
325  };
326
327  rules.image = {
328    filter: 'img',
329
330    replacement: function (content, node) {
331      var alt = cleanAttribute(node.getAttribute('alt'));
332      var src = node.getAttribute('src') || '';
333      var title = cleanAttribute(node.getAttribute('title'));
334      var titlePart = title ? ' "' + title + '"' : '';
335      return src ? '![' + alt + ']' + '(' + src + titlePart + ')' : ''
336    }
337  };
338
339  function cleanAttribute (attribute) {
340    return attribute ? attribute.replace(/(\n+\s*)+/g, '\n') : ''
341  }
342
343  /**
344   * Manages a collection of rules used to convert HTML to Markdown
345   */
346
347  function Rules (options) {
348    this.options = options;
349    this._keep = [];
350    this._remove = [];
351
352    this.blankRule = {
353      replacement: options.blankReplacement
354    };
355
356    this.keepReplacement = options.keepReplacement;
357
358    this.defaultRule = {
359      replacement: options.defaultReplacement
360    };
361
362    this.array = [];
363    for (var key in options.rules) this.array.push(options.rules[key]);
364  }
365
366  Rules.prototype = {
367    add: function (key, rule) {
368      this.array.unshift(rule);
369    },
370
371    keep: function (filter) {
372      this._keep.unshift({
373        filter: filter,
374        replacement: this.keepReplacement
375      });
376    },
377
378    remove: function (filter) {
379      this._remove.unshift({
380        filter: filter,
381        replacement: function () {
382          return ''
383        }
384      });
385    },
386
387    forNode: function (node) {
388      if (node.isBlank) return this.blankRule
389      var rule;
390
391      if ((rule = findRule(this.array, node, this.options))) return rule
392      if ((rule = findRule(this._keep, node, this.options))) return rule
393      if ((rule = findRule(this._remove, node, this.options))) return rule
394
395      return this.defaultRule
396    },
397
398    forEach: function (fn) {
399      for (var i = 0; i < this.array.length; i++) fn(this.array[i], i);
400    }
401  };
402
403  function findRule (rules, node, options) {
404    for (var i = 0; i < rules.length; i++) {
405      var rule = rules[i];
406      if (filterValue(rule, node, options)) return rule
407    }
408    return void 0
409  }
410
411  function filterValue (rule, node, options) {
412    var filter = rule.filter;
413    if (typeof filter === 'string') {
414      if (filter === node.nodeName.toLowerCase()) return true
415    } else if (Array.isArray(filter)) {
416      if (filter.indexOf(node.nodeName.toLowerCase()) > -1) return true
417    } else if (typeof filter === 'function') {
418      if (filter.call(rule, node, options)) return true
419    } else {
420      throw new TypeError('`filter` needs to be a string, array, or function')
421    }
422  }
423
424  /**
425   * The collapseWhitespace function is adapted from collapse-whitespace
426   * by Luc Thevenard.
427   *
428   * The MIT License (MIT)
429   *
430   * Copyright (c) 2014 Luc Thevenard <[email protected]>
431   *
432   * Permission is hereby granted, free of charge, to any person obtaining a copy
433   * of this software and associated documentation files (the "Software"), to deal
434   * in the Software without restriction, including without limitation the rights
435   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
436   * copies of the Software, and to permit persons to whom the Software is
437   * furnished to do so, subject to the following conditions:
438   *
439   * The above copyright notice and this permission notice shall be included in
440   * all copies or substantial portions of the Software.
441   *
442   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
443   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
444   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
445   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
446   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
447   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
448   * THE SOFTWARE.
449   */
450
451  /**
452   * collapseWhitespace(options) removes extraneous whitespace from an the given element.
453   *
454   * @param {Object} options
455   */
456  function collapseWhitespace (options) {
457    var element = options.element;
458    var isBlock = options.isBlock;
459    var isVoid = options.isVoid;
460    var isPre = options.isPre || function (node) {
461      return node.nodeName === 'PRE'
462    };
463
464    if (!element.firstChild || isPre(element)) return
465
466    var prevText = null;
467    var keepLeadingWs = false;
468
469    var prev = null;
470    var node = next(prev, element, isPre);
471
472    while (node !== element) {
473      if (node.nodeType === 3 || node.nodeType === 4) { // Node.TEXT_NODE or Node.CDATA_SECTION_NODE
474        var text = node.data.replace(/[ \r\n\t]+/g, ' ');
475
476        if ((!prevText || / $/.test(prevText.data)) &&
477            !keepLeadingWs && text[0] === ' ') {
478          text = text.substr(1);
479        }
480
481        // `text` might be empty at this point.
482        if (!text) {
483          node = remove(node);
484          continue
485        }
486
487        node.data = text;
488
489        prevText = node;
490      } else if (node.nodeType === 1) { // Node.ELEMENT_NODE
491        if (isBlock(node) || node.nodeName === 'BR') {
492          if (prevText) {
493            prevText.data = prevText.data.replace(/ $/, '');
494          }
495
496          prevText = null;
497          keepLeadingWs = false;
498        } else if (isVoid(node) || isPre(node)) {
499          // Avoid trimming space around non-block, non-BR void elements and inline PRE.
500          prevText = null;
501          keepLeadingWs = true;
502        } else if (prevText) {
503          // Drop protection if set previously.
504          keepLeadingWs = false;
505        }
506      } else {
507        node = remove(node);
508        continue
509      }
510
511      var nextNode = next(prev, node, isPre);
512      prev = node;
513      node = nextNode;
514    }
515
516    if (prevText) {
517      prevText.data = prevText.data.replace(/ $/, '');
518      if (!prevText.data) {
519        remove(prevText);
520      }
521    }
522  }
523
524  /**
525   * remove(node) removes the given node from the DOM and returns the
526   * next node in the sequence.
527   *
528   * @param {Node} node
529   * @return {Node} node
530   */
531  function remove (node) {
532    var next = node.nextSibling || node.parentNode;
533
534    node.parentNode.removeChild(node);
535
536    return next
537  }
538
539  /**
540   * next(prev, current, isPre) returns the next node in the sequence, given the
541   * current and previous nodes.
542   *
543   * @param {Node} prev
544   * @param {Node} current
545   * @param {Function} isPre
546   * @return {Node}
547   */
548  function next (prev, current, isPre) {
549    if ((prev && prev.parentNode === current) || isPre(current)) {
550      return current.nextSibling || current.parentNode
551    }
552
553    return current.firstChild || current.nextSibling || current.parentNode
554  }
555
556  /*
557   * Set up window for Node.js
558   */
559
560  var root = (typeof window !== 'undefined' ? window : {});
561
562  /*
563   * Parsing HTML strings
564   */
565
566  function canParseHTMLNatively () {
567    var Parser = root.DOMParser;
568    var canParse = false;
569
570    // Adapted from https://gist.github.com/1129031
571    // Firefox/Opera/IE throw errors on unsupported types
572    try {
573      // WebKit returns null on unsupported types
574      if (new Parser().parseFromString('', 'text/html')) {
575        canParse = true;
576      }
577    } catch (e) {}
578
579    return canParse
580  }
581
582  function createHTMLParser () {
583    var Parser = function () {};
584
585    {
586      if (shouldUseActiveX()) {
587        Parser.prototype.parseFromString = function (string) {
588          var doc = new window.ActiveXObject('htmlfile');
589          doc.designMode = 'on'; // disable on-page scripts
590          doc.open();
591          doc.write(string);
592          doc.close();
593          return doc
594        };
595      } else {
596        Parser.prototype.parseFromString = function (string) {
597          var doc = document.implementation.createHTMLDocument('');
598          doc.open();
599          doc.write(string);
600          doc.close();
601          return doc
602        };
603      }
604    }
605    return Parser
606  }
607
608  function shouldUseActiveX () {
609    var useActiveX = false;
610    try {
611      document.implementation.createHTMLDocument('').open();
612    } catch (e) {
613      if (root.ActiveXObject) useActiveX = true;
614    }
615    return useActiveX
616  }
617
618  var HTMLParser = canParseHTMLNatively() ? root.DOMParser : createHTMLParser();
619
620  function RootNode (input, options) {
621    var root;
622    if (typeof input === 'string') {
623      var doc = htmlParser().parseFromString(
624        // DOM parsers arrange elements in the <head> and <body>.
625        // Wrapping in a custom element ensures elements are reliably arranged in
626        // a single element.
627        '<x-turndown id="turndown-root">' + input + '</x-turndown>',
628        'text/html'
629      );
630      root = doc.getElementById('turndown-root');
631    } else {
632      root = input.cloneNode(true);
633    }
634    collapseWhitespace({
635      element: root,
636      isBlock: isBlock,
637      isVoid: isVoid,
638      isPre: options.preformattedCode ? isPreOrCode : null
639    });
640
641    return root
642  }
643
644  var _htmlParser;
645  function htmlParser () {
646    _htmlParser = _htmlParser || new HTMLParser();
647    return _htmlParser
648  }
649
650  function isPreOrCode (node) {
651    return node.nodeName === 'PRE' || node.nodeName === 'CODE'
652  }
653
654  function Node (node, options) {
655    node.isBlock = isBlock(node);
656    node.isCode = node.nodeName === 'CODE' || node.parentNode.isCode;
657    node.isBlank = isBlank(node);
658    node.flankingWhitespace = flankingWhitespace(node, options);
659    return node
660  }
661
662  function isBlank (node) {
663    return (
664      !isVoid(node) &&
665      !isMeaningfulWhenBlank(node) &&
666      /^\s*$/i.test(node.textContent) &&
667      !hasVoid(node) &&
668      !hasMeaningfulWhenBlank(node)
669    )
670  }
671
672  function flankingWhitespace (node, options) {
673    if (node.isBlock || (options.preformattedCode && node.isCode)) {
674      return { leading: '', trailing: '' }
675    }
676
677    var edges = edgeWhitespace(node.textContent);
678
679    // abandon leading ASCII WS if left-flanked by ASCII WS
680    if (edges.leadingAscii && isFlankedByWhitespace('left', node, options)) {
681      edges.leading = edges.leadingNonAscii;
682    }
683
684    // abandon trailing ASCII WS if right-flanked by ASCII WS
685    if (edges.trailingAscii && isFlankedByWhitespace('right', node, options)) {
686      edges.trailing = edges.trailingNonAscii;
687    }
688
689    return { leading: edges.leading, trailing: edges.trailing }
690  }
691
692  function edgeWhitespace (string) {
693    var m = string.match(/^(([ \t\r\n]*)(\s*))(?:(?=\S)[\s\S]*\S)?((\s*?)([ \t\r\n]*))$/);
694    return {
695      leading: m[1], // whole string for whitespace-only strings
696      leadingAscii: m[2],
697      leadingNonAscii: m[3],
698      trailing: m[4], // empty for whitespace-only strings
699      trailingNonAscii: m[5],
700      trailingAscii: m[6]
701    }
702  }
703
704  function isFlankedByWhitespace (side, node, options) {
705    var sibling;
706    var regExp;
707    var isFlanked;
708
709    if (side === 'left') {
710      sibling = node.previousSibling;
711      regExp = / $/;
712    } else {
713      sibling = node.nextSibling;
714      regExp = /^ /;
715    }
716
717    if (sibling) {
718      if (sibling.nodeType === 3) {
719        isFlanked = regExp.test(sibling.nodeValue);
720      } else if (options.preformattedCode && sibling.nodeName === 'CODE') {
721        isFlanked = false;
722      } else if (sibling.nodeType === 1 && !isBlock(sibling)) {
723        isFlanked = regExp.test(sibling.textContent);
724      }
725    }
726    return isFlanked
727  }
728
729  var reduce = Array.prototype.reduce;
730  var escapes = [
731    [/\\/g, '\\\\'],
732    [/\*/g, '\\*'],
733    [/^-/g, '\\-'],
734    [/^\+ /g, '\\+ '],
735    [/^(=+)/g, '\\$1'],
736    [/^(#{1,6}) /g, '\\$1 '],
737    [/`/g, '\\`'],
738    [/^~~~/g, '\\~~~'],
739    [/\[/g, '\\['],
740    [/\]/g, '\\]'],
741    [/^>/g, '\\>'],
742    [/_/g, '\\_'],
743    [/^(\d+)\. /g, '$1\\. ']
744  ];
745
746  function TurndownService (options) {
747    if (!(this instanceof TurndownService)) return new TurndownService(options)
748
749    var defaults = {
750      rules: rules,
751      headingStyle: 'setext',
752      hr: '* * *',
753      bulletListMarker: '*',
754      codeBlockStyle: 'indented',
755      fence: '```',
756      emDelimiter: '_',
757      strongDelimiter: '**',
758      linkStyle: 'inlined',
759      linkReferenceStyle: 'full',
760      br: '  ',
761      preformattedCode: false,
762      blankReplacement: function (content, node) {
763        return node.isBlock ? '\n\n' : ''
764      },
765      keepReplacement: function (content, node) {
766        return node.isBlock ? '\n\n' + node.outerHTML + '\n\n' : node.outerHTML
767      },
768      defaultReplacement: function (content, node) {
769        return node.isBlock ? '\n\n' + content + '\n\n' : content
770      }
771    };
772    this.options = extend({}, defaults, options);
773    this.rules = new Rules(this.options);
774  }
775
776  TurndownService.prototype = {
777    /**
778     * The entry point for converting a string or DOM node to Markdown
779     * @public
780     * @param {String|HTMLElement} input The string or DOM node to convert
781     * @returns A Markdown representation of the input
782     * @type String
783     */
784
785    turndown: function (input) {
786      if (!canConvert(input)) {
787        throw new TypeError(
788          input + ' is not a string, or an element/document/fragment node.'
789        )
790      }
791
792      if (input === '') return ''
793
794      var output = process.call(this, new RootNode(input, this.options));
795      return postProcess.call(this, output)
796    },
797
798    /**
799     * Add one or more plugins
800     * @public
801     * @param {Function|Array} plugin The plugin or array of plugins to add
802     * @returns The Turndown instance for chaining
803     * @type Object
804     */
805
806    use: function (plugin) {
807      if (Array.isArray(plugin)) {
808        for (var i = 0; i < plugin.length; i++) this.use(plugin[i]);
809      } else if (typeof plugin === 'function') {
810        plugin(this);
811      } else {
812        throw new TypeError('plugin must be a Function or an Array of Functions')
813      }
814      return this
815    },
816
817    /**
818     * Adds a rule
819     * @public
820     * @param {String} key The unique key of the rule
821     * @param {Object} rule The rule
822     * @returns The Turndown instance for chaining
823     * @type Object
824     */
825
826    addRule: function (key, rule) {
827      this.rules.add(key, rule);
828      return this
829    },
830
831    /**
832     * Keep a node (as HTML) that matches the filter
833     * @public
834     * @param {String|Array|Function} filter The unique key of the rule
835     * @returns The Turndown instance for chaining
836     * @type Object
837     */
838
839    keep: function (filter) {
840      this.rules.keep(filter);
841      return this
842    },
843
844    /**
845     * Remove a node that matches the filter
846     * @public
847     * @param {String|Array|Function} filter The unique key of the rule
848     * @returns The Turndown instance for chaining
849     * @type Object
850     */
851
852    remove: function (filter) {
853      this.rules.remove(filter);
854      return this
855    },
856
857    /**
858     * Escapes Markdown syntax
859     * @public
860     * @param {String} string The string to escape
861     * @returns A string with Markdown syntax escaped
862     * @type String
863     */
864
865    escape: function (string) {
866      return escapes.reduce(function (accumulator, escape) {
867        return accumulator.replace(escape[0], escape[1])
868      }, string)
869    }
870  };
871
872  /**
873   * Reduces a DOM node down to its Markdown string equivalent
874   * @private
875   * @param {HTMLElement} parentNode The node to convert
876   * @returns A Markdown representation of the node
877   * @type String
878   */
879
880  function process (parentNode) {
881    var self = this;
882    return reduce.call(parentNode.childNodes, function (output, node) {
883      node = new Node(node, self.options);
884
885      var replacement = '';
886      if (node.nodeType === 3) {
887        replacement = node.isCode ? node.nodeValue : self.escape(node.nodeValue);
888      } else if (node.nodeType === 1) {
889        replacement = replacementForNode.call(self, node);
890      }
891
892      return join(output, replacement)
893    }, '')
894  }
895
896  /**
897   * Appends strings as each rule requires and trims the output
898   * @private
899   * @param {String} output The conversion output
900   * @returns A trimmed version of the ouput
901   * @type String
902   */
903
904  function postProcess (output) {
905    var self = this;
906    this.rules.forEach(function (rule) {
907      if (typeof rule.append === 'function') {
908        output = join(output, rule.append(self.options));
909      }
910    });
911
912    return output.replace(/^[\t\r\n]+/, '').replace(/[\t\r\n\s]+$/, '')
913  }
914
915  /**
916   * Converts an element node to its Markdown equivalent
917   * @private
918   * @param {HTMLElement} node The node to convert
919   * @returns A Markdown representation of the node
920   * @type String
921   */
922
923  function replacementForNode (node) {
924    var rule = this.rules.forNode(node);
925    var content = process.call(this, node);
926    var whitespace = node.flankingWhitespace;
927    if (whitespace.leading || whitespace.trailing) content = content.trim();
928    return (
929      whitespace.leading +
930      rule.replacement(content, node, this.options) +
931      whitespace.trailing
932    )
933  }
934
935  /**
936   * Joins replacement to the current output with appropriate number of new lines
937   * @private
938   * @param {String} output The current conversion output
939   * @param {String} replacement The string to append to the output
940   * @returns Joined output
941   * @type String
942   */
943
944  function join (output, replacement) {
945    var s1 = trimTrailingNewlines(output);
946    var s2 = trimLeadingNewlines(replacement);
947    var nls = Math.max(output.length - s1.length, replacement.length - s2.length);
948    var separator = '\n\n'.substring(0, nls);
949
950    return s1 + separator + s2
951  }
952
953  /**
954   * Determines whether an input can be converted
955   * @private
956   * @param {String|HTMLElement} input Describe this parameter
957   * @returns Describe what it returns
958   * @type String|Object|Array|Boolean|Number
959   */
960
961  function canConvert (input) {
962    return (
963      input != null && (
964        typeof input === 'string' ||
965        (input.nodeType && (
966          input.nodeType === 1 || input.nodeType === 9 || input.nodeType === 11
967        ))
968      )
969    )
970  }
971
972  return TurndownService;
973
974}());

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