parseInt is a function. A prototype property is automatically created for every function. Function().prototype; // parseInt does not have a prototype property. In order to be a Function, parseInt must have a prototype property. A function that does not have a prototype property does not conform to the Function interface; it should not be considered a function. This applies to all built-in functions. Math.round, et c. See also bug 14547
ECMA 262 3rd Ed, Section 15 paragraph 9 says:- "None of the built-in functions described in this section shall implement the internal [[Construct]] method unless otherwise specified in the description of a particular function. None of the built-in functions described in this section shall initially have a prototype property unless otherwise specified in the description of a particular function."