See if an object has a property

hasProperty.js

var has = function (obj, property) {
  var tree = obj,
      split = property.split('.'),
      last = split.pop();

  while (next = split.shift()) {
    tree = tree[next];
    if (tree === undefined) return false;
  }

  return tree[last] === undefined ? false : true;
};

test.js

console.assert( has(o, 'foo'), 'foo');
console.assert( has(o, 'foo.bar'), 'foo.bar' );

console.assert( !has(o, 'bar'), 'bar' );
console.assert( !has(o, 'foo.bar.baz'), 'foo.bar.baz' );

I fear that the comparison with undefined after using the [] accessor on an object is not the most correct way to establish whether or not an object has a property. In JavaScript it is possible for someone to assign the value of undefined onto a variable or property.

While technically the object would then have the property, this code would claim it does not.

Consider Resig's answer in this StackOverflow question on the topic:
http://stackoverflow.com/questions/135448/how-do-i-check-to-see-if-an-object-has-a-property-in-javascript