htmltomarkdown.js

htmltomarkdown.js

var toMarkdown = function(string) {
    var ELEMENTS = [{
      patterns: 'p',
      replacement: function(str, attrs, innerHTML) {
        return innerHTML ? '\n\n' + innerHTML + '\n' : '';
      }
    }, {
      patterns: 'br',
      type: 'void',
      replacement: '\n'
    }, {
      patterns: 'h([1-6])',
      replacement: function(str, hLevel, attrs, innerHTML) {
        var hPrefix = '';
        for(var i = 0; i < hLevel; i++) {
          hPrefix += '#';
        }
        return '\n\n' + hPrefix + ' ' + innerHTML + '\n';
      }
    }, {
      patterns: 'hr',
      type: 'void',
      replacement: '\n\n* * *\n'
    }, {
      patterns: 'a',
      replacement: function(str, attrs, innerHTML) {
        var href = attrs.match(attrRegExp('href')),
          title = attrs.match(attrRegExp('title'));
        return href ? '[' + innerHTML + ']' + '(' + href[1] + (title && title[1] ? ' "' + title[1] + '"' : '') + ')' : str;
      }
    }, {
      patterns: ['b', 'strong'],
      replacement: function(str, attrs, innerHTML) {
        return innerHTML ? '**' + innerHTML + '**' : '';
      }
    }, {
      patterns: ['i', 'em'],
      replacement: function(str, attrs, innerHTML) {
        return innerHTML ? '_' + innerHTML + '_' : '';
      }
    }, {
      patterns: 'code',
      replacement: function(str, attrs, innerHTML) {
        return innerHTML ? '`' + innerHTML + '`' : '';
      }
    },
    {
      patterns: 'pre',
      replacement: function(str, attrs, innerHTML) {
        return innerHTML ? '`' + innerHTML + '`' : '';
      }
    }, 
    {
      patterns: 'img',
      type: 'void',
      replacement: function(str, attrs, innerHTML) {
        var src = attrs.match(attrRegExp('src')),
          alt = attrs.match(attrRegExp('alt')),
          title = attrs.match(attrRegExp('title'));
        return '![' + (alt && alt[1] ? alt[1] : '') + ']' + '(' + src[1] + (title && title[1] ? ' "' + title[1] + '"' : '') + ')';
      }
    },
    {
      patterns: 'style',
      replacement: function(str, attrs, innerHTML) {
        return '';
      }
    },
    {
      patterns: 'script',
      replacement: function(str, attrs, innerHTML) {
        return '';
      }
    },
    {
      patterns: 'div',
      replacement: function(str, attrs, innerHTML) {
        return innerHTML;
      }
    }
    ];

    for(var i = 0, len = ELEMENTS.length; i < len; i++) {
      if(typeof ELEMENTS[i].patterns === 'string') {
        string = replaceEls(string, {
          tag: ELEMENTS[i].patterns,
          replacement: ELEMENTS[i].replacement,
          type: ELEMENTS[i].type
        });
      } else {
        for(var j = 0, pLen = ELEMENTS[i].patterns.length; j < pLen; j++) {
          string = replaceEls(string, {
            tag: ELEMENTS[i].patterns[j],
            replacement: ELEMENTS[i].replacement,
            type: ELEMENTS[i].type
          });
        }
      }
    }

    function replaceEls(html, elProperties) {
      var pattern = elProperties.type === 'void' ? '<' + elProperties.tag + '\\b([^>]*)\\/?>' : '<' + elProperties.tag + '\\b([^>]*)>([\\s\\S]*?)<\\/' + elProperties.tag + '>',
        regex = new RegExp(pattern, 'gi'),
        markdown = '';
      if(typeof elProperties.replacement === 'string') {
        markdown = html.replace(regex, elProperties.replacement);
      } else {
        markdown = html.replace(regex, function(str, p1, p2, p3) {
          return elProperties.replacement.call(this, str, p1, p2, p3);
        });
      }
      return markdown;
    }

    function attrRegExp(attr) {
      return new RegExp(attr + '\\s*=\\s*["\']?([^"\']*)["\']?', 'i');
    }

    // Pre code blocks
    string = string.replace(/<pre\b[^>]*>`([\s\S]*)`<\/pre>/gi, function(str, innerHTML) {
      innerHTML = innerHTML.replace(/^\t+/g, '  '); // convert tabs to spaces (you know it makes sense)
      innerHTML = innerHTML.replace(/\n/g, '\n    ');
      return '\n\n    ' + innerHTML + '\n';
    });

    // Lists
    // Escape numbers that could trigger an ol
    // If there are more than three spaces before the code, it would be in a pre tag
    // Make sure we are escaping the period not matching any character
    string = string.replace(/^(\s{0,3}\d+)\. /g, '$1\\. ');

    // Converts lists that have no child lists (of same type) first, then works it's way up
    var noChildrenRegex = /<(ul|ol)\b[^>]*>(?:(?!<ul|<ol)[\s\S])*?<\/\1>/gi;
    while(string.match(noChildrenRegex)) {
      string = string.replace(noChildrenRegex, function(str) {
        return replaceLists(str);
      });
    }

    function replaceLists(html) {

      html = html.replace(/<(ul|ol)\b[^>]*>([\s\S]*?)<\/\1>/gi, function(str, listType, innerHTML) {
        var lis = innerHTML.split('</li>');
        lis.splice(lis.length - 1, 1);

        for(i = 0, len = lis.length; i < len; i++) {
          if(lis[i]) {
            var prefix = (listType === 'ol') ? (i + 1) + ".  " : "*   ";
            lis[i] = lis[i].replace(/\s*<li[^>]*>([\s\S]*)/i, function(str, innerHTML) {

              innerHTML = innerHTML.replace(/^\s+/, '');
              innerHTML = innerHTML.replace(/\n\n/g, '\n\n    ');
              // indent nested lists
              innerHTML = innerHTML.replace(/\n([ ]*)+(\*|\d+\.) /g, '\n$1    $2 ');
              return prefix + innerHTML;
            });
          }
        }
        return lis.join('\n');
      });
      return '\n\n' + html.replace(/[ \t]+\n|\s+$/g, '');
    }

    // Blockquotes
    var deepest = /<blockquote\b[^>]*>((?:(?!<blockquote)[\s\S])*?)<\/blockquote>/gi;
    while(string.match(deepest)) {
      string = string.replace(deepest, function(str) {
        return replaceBlockquotes(str);
      });
    }

    function replaceBlockquotes(html) {
      html = html.replace(/<blockquote\b[^>]*>([\s\S]*?)<\/blockquote>/gi, function(str, inner) {
        inner = inner.replace(/^\s+|\s+$/g, '');
        inner = cleanUp(inner);
        inner = inner.replace(/^/gm, '> ');
        inner = inner.replace(/^(>([ \t]{2,}>)+)/gm, '> >');
        return inner;
      });
      return html;
    }

    function cleanUp(string) {
      string = string.replace(/^[\t\r\n]+|[\t\r\n]+$/g, ''); // trim leading/trailing whitespace
      string = string.replace(/\n\s+\n/g, '\n\n');
      string = string.replace(/\n{3,}/g, '\n\n'); // limit consecutive linebreaks to 2
      return string;
    }

    return cleanUp(string);
  };