JavaScript object prototype Poisoning

Question

I was trying to learn how object.prototype function in javascript then I came across this snippet of code .which I don't understand?

// Poisoning Object.prototype
Object.prototype.bar = 1;
var foo = {goo: undefined};

foo.bar; // 1
'bar' in foo; // true

foo.hasOwnProperty('bar'); // false
foo.hasOwnProperty('goo'); // true

foo has the property bar which is defined in the line number 3 and having the value of undefined .Please guide then why foo.hasOwnProperty('bar') returns false in this case

Answer 1

All objects in JavaScript are descended from Object. all objects inherit methods and properties from Object.prototype.

In your example when you try to get the foo.bar, it doesn't find bar in the foo, so it is going to the prototype of the foo and tries to find it there.

hasOwnProperty - only checks a property which is exactly in the your foo.

Here is what your foo looks like

For deep understanding you can read this chapter.

You Don't Know JS