Space and time of local variable vs. this

@Gordon, what's your implementation-knowing 'guess'? ...space / memory footprint, time / performance?

var obj =
{ property:123
, funWithThis: function() {
    // function/method using 'this' in body
    // lots of lots this.something(); this.somethingThat(); ...
    return this.property;
  }
, funWithLocalVariable: function() {
    // function/method using 'var _ that references this' in body
    var _ = this;
    // lots of lots _.something(); _.somethingThat(); ...
  }
  return _;
};