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;
};