// Poisoning Object.prototype
Object.prototype.bar = 1;
var foo = {goo: undefined};

foo.bar; // 1
'bar' in foo; // true

foo.hasOwnProperty('bar'); // false
foo.hasOwnProperty('goo'); // true

var foo = {
 hasOwnProperty: function() {
 return false;
 },
 bar: 'Here be dragons'
};

foo.hasOwnProperty('bar'); // always returns false

// Use another Object's hasOwnProperty and call it with 'this' set to foo
({}).hasOwnProperty.call(foo, 'bar'); // true

// It's also possible to use hasOwnProperty from the Object
// prototype for this purpose
Object.prototype.hasOwnProperty.call(foo, 'bar'); // true

o = new Object();
o.prop = 'exists';
o.hasOwnProperty('prop');       // 返回 true
o.hasOwnProperty('toString');     // 返回 false
o.hasOwnProperty('hasOwnProperty');  // 返回 false

var foo = {
  hasOwnProperty: function() {
    return false;
  },
  bar: 'Here be dragons'
};

foo.hasOwnProperty('bar'); // 始終返回 false

({}).hasOwnProperty.call(foo, 'bar'); // true
// 或者：
Object.prototype.hasOwnProperty.call(foo, 'bar'); // true