gistfile1.js

(function(){
  function X(a, b) {
    this.a = a;
    this.b = b;
  }
  var a = new X(1, 1);
  var b = new X(1, 1);
  alert('[first] ' + (a == b));

  X.prototype.toString = function() {
    return 'a:[' + this.a + '] b:[' + this.b + ']';
  };
  alert('[toString] ' + (a == b));

  X.prototype.valueOf = function() {
    return 'a:[' + this.a + '] b:[' + this.b + ']';
  };
  alert('[valueOf] ' + (a == b));
})()