Для ИЕ:

if (!Object.keys) {
  Object.keys = (function () {
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        hasDontEnumBug = !({toString: null}).propertyIsEnumerable('toString'),
        dontEnums = [
          'toString',
          'toLocaleString',
          'valueOf',
          'hasOwnProperty',
          'isPrototypeOf',
          'propertyIsEnumerable',
          'constructor'
        ],
        dontEnumsLength = dontEnums.length
 
    return function (obj) {
      if (typeof obj !== 'object' && typeof obj !== 'function' || obj === null) throw new TypeError('Object.keys called on non-object')
 
      var result = []
 
      for (var prop in obj) {
        if (hasOwnProperty.call(obj, prop)) result.push(prop)
      }
 
      if (hasDontEnumBug) {
        for (var i=0; i < dontEnumsLength; i++) {
          if (hasOwnProperty.call(obj, dontEnums[i])) result.push(dontEnums[i])
        }
      }
      return result
    }
  })()
};

взято от сюда: https://developer.mozilla.org/en-US/...ts/Object/keys

//Для начала создадим счетчик:
var cnt = 0;
for(var p in obj) cnt++;
console.log(cnt);