A.13. hasOwnProperty

In Chapter 3, the hasOwnProperty method was offered as a filter to work around a problem with the for in statement. Unfortunately, hasOwnProperty is a method, not an operator, so in any object it could be replaced with a different function or even a value that is not a function:

var name;
another_stooge.hasOwnProperty = null;       // trouble
for (name in another_stooge) {
    if (another_stooge.hasOwnProperty(name)) { // boom
        document.writeln(name + ': ' + another_stooge[name]);
    }
}