javascript - check for undefined in hasownproperty in modenizer -

i going through modenizers own version of hasownproperty function , came across following script:

_hasownproperty = ({}).hasownproperty, hasownprop;  if ( !is(_hasownproperty, 'undefined') && !is(_hasownproperty.call, 'undefined') ) {   hasownprop = function (object, property) {     return _hasownproperty.call(object, property);   }; } else {   hasownprop = function (object, property) {     // diff below  line means i.e. object.constructor.prototype[property] ask j     return ((property in object) && is(object.constructor.prototype[property], 'undefined'));   }; } 

if secound hasownprop function, see following check inside:

is(object.constructor.prototype[property], 'undefined') 

the condition defined in modernizer:

function is( obj, type ) {         return typeof obj === type;     } 

but don't understand check, below:

is(object.constructor.prototype[property], 'undefined'); 

why check undefined on constructor of property ? whats sense make ? can explain ?