JavaScript version of WordPress wpautop function

wpautop.js

// source: https://github.com/andymantell/node-wpautop
  function _autop_newline_preservation_helper( matches ) {
    return matches[ 0 ].replace( "\n", "<WPPreserveNewline />" );
  }

  function wpautop( pee, br ) {
    if ( typeof (br) === 'undefined' ) {
      br = true;
    }

    var pre_tags = {};
    if ( pee.trim() === '' ) {
      return '';
    }

    pee = pee + "\n"; // just to make things a little easier, pad the end
    if ( pee.indexOf( '<pre' ) > -1 ) {
      var pee_parts = pee.split( '</pre>' );
      var last_pee  = pee_parts.pop();
      pee           = '';
      pee_parts.forEach( function( pee_part, index ) {
        var start = pee_part.indexOf( '<pre' );

        // Malformed html?
        if ( start === -1 ) {
          pee += pee_part;
          return;
        }

        var name         = "<pre wp-pre-tag-" + index + "></pre>";
        pre_tags[ name ] = pee_part.substr( start ) + '</pre>';
        pee += pee_part.substr( 0, start ) + name;

      } );

      pee += last_pee;
    }

    pee = pee.replace( /<br \/>\s*<br \/>/, "\n\n" );

    // Space things out a little
    var allblocks = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|form|map|area|blockquote|address|math|style|p|h[1-6]|hr|fieldset|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)';
    pee           = pee.replace( new RegExp( '(<' + allblocks + '[^>]*>)', 'gmi' ), "\n$1" );
    pee           = pee.replace( new RegExp( '(</' + allblocks + '>)', 'gmi' ), "$1\n\n" );
    pee           = pee.replace( /\r\n|\r/, "\n" ); // cross-platform newlines

    if ( pee.indexOf( '<option' ) > -1 ) {
      // no P/BR around option
      pee = pee.replace( /\s*<option'/gmi, '<option' );
      pee = pee.replace( /<\/option>\s*/gmi, '</option>' );
    }

    if ( pee.indexOf( '</object>' ) > -1 ) {
      // no P/BR around param and embed
      pee = pee.replace( /(<object[^>]*>)\s*/gmi, '$1' );
      pee = pee.replace( /\s*<\/object>/gmi, '</object>' );
      pee = pee.replace( /\s*(<\/?(?:param|embed)[^>]*>)\s*/gmi, '$1' );
    }

    if ( pee.indexOf( '<source' ) > -1 || pee.indexOf( '<track' ) > -1 ) {
      // no P/BR around source and track
      pee = pee.replace( /([<\[](?:audio|video)[^>\]]*[>\]])\s*/gmi, '$1' );
      pee = pee.replace( /\s*([<\[]\/(?:audio|video)[>\]])/gmi, '$1' );
      pee = pee.replace( /\s*(<(?:source|track)[^>]*>)\s*/gmi, '$1' );
    }

    pee = pee.replace( /\n\n+/gmi, "\n\n" ); // take care of duplicates

    // make paragraphs, including one at the end
    var pees = pee.split( /\n\s*\n/ );
    pee      = '';
    pees.forEach( function( tinkle ) {
      pee += '<p>' + tinkle.replace( /^\s+|\s+$/g, '' ) + "</p>\n";
    } );

    pee = pee.replace( /<p>\s*<\/p>/gmi, '' ); // under certain strange conditions it could create a P of entirely whitespace
    pee = pee.replace( /<p>([^<]+)<\/(div|address|form)>/gmi, "<p>$1</p></$2>" );
    pee = pee.replace( new RegExp( '<p>\s*(</?' + allblocks + '[^>]*>)\s*</p>', 'gmi' ), "$1", pee ); // don't pee all over a tag
    pee = pee.replace( /<p>(<li.+?)<\/p>/gmi, "$1" ); // problem with nested lists
    pee = pee.replace( /<p><blockquote([^>]*)>/gmi, "<blockquote$1><p>" );
    pee = pee.replace( /<\/blockquote><\/p>/gmi, '</p></blockquote>' );
    pee = pee.replace( new RegExp( '<p>\s*(</?' + allblocks + '[^>]*>)', 'gmi' ), "$1" );
    pee = pee.replace( new RegExp( '(</?' + allblocks + '[^>]*>)\s*</p>', 'gmi' ), "$1" );

    if ( br ) {
      pee = pee.replace( /<(script|style)(?:.|\n)*?<\/\\1>/gmi, _autop_newline_preservation_helper ); // /s modifier from php PCRE regexp replaced with (?:.|\n)
      pee = pee.replace( /(<br \/>)?\s*\n/gmi, "<br />\n" ); // optionally make line breaks
      pee = pee.replace( '<WPPreserveNewline />', "\n" );
    }

    pee = pee.replace( new RegExp( '(</?' + allblocks + '[^>]*>)\s*<br />', 'gmi' ), "$1" );
    pee = pee.replace( /<br \/>(\s*<\/?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)/gmi, '$1' );
    pee = pee.replace( /\n<\/p>$/gmi, '</p>' );

    if ( Object.keys( pre_tags ).length ) {
      pee = pee.replace( new RegExp( Object.keys( pre_tags ).join( '|' ), "gi" ), function( matched ) {
        return pre_tags[ matched ];
      } );
    }

    return pee;
  }