understanding modernizer feature detection script

understanding modernizer feature detection script

Hey guys , have a look at the below script : 

  1.   Mod = {};
  2.         attr = {};
  3.         Mod['input'] = (function(prop){
  4.             for (var i = 0; i < prop.length; i++) {
  5.                attr[prop[i]] = !!(prop[i] in inputElem);
  6.             }
  7.             return attr;. 
  8.         })('autocomplete autofocus list placeholder max min multiple pattern required step'.split(' '))

  10.         console.log(Mod['input']);
its a feature detection script from modinizer , i just abstracted that code and modified it a bit , basically it stores all the input attibutes supported in a users browser in a object literal format in a variable . 

my question is about the below check performed, 

  1. !!(prop[i] in inputElem)
i understand that the property is being checked against the element and than converted to a boolean , i just wanted to know , is this a reliable way to check , i mean to use the in operator to check if a attribute is supported in a given users browser for a given element ?