Javascript get item in object code

Question

So I have some Javascript code that resembles the following:

var mylibrary = new (function ()
{
 this._getLibraryObj = function ()
 {
 var newLibraryObj = {};
 var libraryData = window.specifiedLibraryData;
 // Add head librarian details
 // open library
 // etc. etc. turn into an object from data
 return newLibraryObj ;
 };
 this.item = function (item)
 {
 if (this.obj && item in this.obj)
 {
 return this.obj[item];
 }
 else
 {
 this.obj = this._getLibraryObj();
 if (item in this.obj)
 {
 return this.obj[item];
 }
 return null;
 }
 };
 return this;
})();

What annoys me is that this.item(item) function repeats the item in this.obj[item] and I find it a little hard to read. I was hoping for it to not have to run _getLibraryObj too often.

Question: How would you rewrite this.item() to be short and sweet (DRY and readable)?

EDIT:- From alex's post I realised I left out one constraint: If the item isn't in the library object then it might need to _getLibraryObj() again as the data may have changed

Solution:- I ended up using @Alex Nolan's fifth example (with || instead of && I find it easier to read.):

this.item = function(item)
{
 if(!this.obj || !item in this.obj)
 {
 this.obj = this._getLibraryObj();
 }
 return this.obj[item] || null;
}

Answer 1

Another downfall of your this.item() function is that if item isn't in this.obj, this._getLibraryObj() will be called every time.

Try

this.item = function(item) {
 if (this.obj) {
 return this.obj[item] || null;
 } else {
 this.obj = this._getLibraryObj();
 return this.item(item);
 }
};

Or if you want it even more minimal:

this.item = function(item) {
 if (this.obj) 
 return this.obj[item] || null;
 this.obj = this._getLibraryObj();
 return this.item(item);
};

If you switch up the statements a little bit you get the most readable IMHO:

this.item = function(item) {
 if (!this.obj) 
 this.obj = this._getLibraryObj();
 return this.obj[item] || null;
};

One final way to do it would be to do:

this.item = function(item) {
 this.obj = this.obj || this._getLibraryObj();
 return this.obj[item] || null;
};

EDIT:

In light of your comment about needing to re-call getLibraryObj

this.item = function(item) {
 if (!(this.obj && item in this.obj))
 this.obj = this._getLibraryObj();
 return this.obj[item] || null;
};

or:

this.item = function(item) {
 this.obj = this.obj && item in this.obj ? this.obj : this._getLibraryObj();
 return this.obj[item] || null;
};

or a one-liner:

this.item = function(item) {
 return (this.obj = (this.obj && item in this.obj ? this.obj : this._getLibraryObj()))[item] || null;
};

• James Khoury: Sorry I left one thing out. If the item isn't in the library object then it might need to _getLibraryObj() again as the data may have changed. I do really like that "final way" Nice and simple ... how could I have not thought of it!?
• James Khoury: I guess I could put an if(!item in this.obj){ this.obj = this._getLibraryObj();} or use the second last example and change the if to if(!this.obj || !item in this.obj) (just thought of a one liner: return item in (this.obj = this.obj || this._getLibraryObj()) ? this.obj[item] : (this.obj = this._getLibraryObj())[item] || null;)