detect_main_content.js

(function detectMainContent(){
  // based on JimmyWales http://d.hatena.ne.jp/ofk/20101123/1290439104
  var scoreCalc = function(elm){
    var nodeTable = {
      "div": 0,
      "article": 50,
      "section": 5
    };
    var clsTable = {
      "content": 5,
      "entry": 5,
      "columns": 5, // techcrunch
      "post": 5,
      "main": 1,
      "body": 1,
      "article": 10,
      "sidebar": -10,
      "header": -10,
      "footer": -10,
      "wrapper": -10,
      "container": -10
    }
    var score = nodeTable[elm.nodeName.toLowerCase()];
    if(elm.className.length > 0){
      score += 1;
    }
    if(elm.getAttribute('id')){
      score += 1;
    }
    for(var cls in clsTable){
      var id = (elm.getAttribute('id') || "").toLowerCase();
      var klass = elm.className.toLowerCase();
      if(klass.indexOf(cls) > -1){
        score += clsTable[cls];
      }
      if(id.indexOf(cls) > -1){
        score += clsTable[cls];
      }
      if(id == cls){
        score += clsTable[cls] * 3;
      }
      if(klass == cls){
        score += clsTable[cls] * 2;
      }
    }
    return score;
  }
  var elements = Array.prototype.slice.call(document.querySelectorAll('div, article, section'));
  var mostImportant = {
    elm: document.querySelector('body'),
    square: 0,
    score: 0
  };
  elements.forEach(function(elm){
    var score = scoreCalc(elm);
    var b = elm.getBoundingClientRect();
    var square = b.height * b.width;
    if(mostImportant.score < score){
      mostImportant = {
        elm: elm,
        score: score,
        square: square
      }
    }else if(mostImportant.score == score){
      if(mostImportant.square < square){
        mostImportant = {
          elm: elm,
          score: score,
          square: square
        }
      }
    }
  });
  // mostImportant.elm.setAttribute('style', 'border: 5px solid red;');
  return mostImportant.elm;
})();