commenter.js

var comments = [];

function digDeeper( el, i ){
  if ( el.nodeType === 8 ){
    comments.push( el.nodeValue.replace( /^\s*|\s*$/g, '' ));
    return;
  }

  if ( ! el || ! el.childNodes || ! el.childNodes.length ){
    return;
  }

  for ( i = el.childNodes.length; i--; ){
    digDeeper( el.childNodes[ i ]);
  }
}

digDeeper( document );

console.warn( comments );