gistfile1.js

//document own properties
console.log(Object.keys(document).sort());

//document own properties & inherited properties
var documentPropertiesIncludeInherited = [];
for(var p in document) { documentPropertiesIncludeInherited.push(p); }
console.log(documentPropertiesIncludeInherited.sort());

//document inherited properties only
var documentPropertiesOnlyInherited = [];
for(var p in document) { 
    if(!document.hasOwnProperty(p)){
        documentPropertiesOnlyInherited.push(p);        
    }
}
console.log(documentPropertiesOnlyInherited.sort())

//document own properties & own non-enumerable
console.log(Object.getOwnPropertyNames(document).sort());

//document own non-enumerable
​console.log(_.difference(Object.getOwnPropertyNames(document),Object.keys(document)).sort());​

what is the meaning of "if(!document.hasOwnProperty(p)){" this line ? I could not understand ! (exclamation mark)