How to check undefined variable javascript?

My Javascript is like this :

<script type="text/javascript">

     var priceJson = '[{"@attributes":{"Code":"SGL","Total":"400000"},"DayPrice":{"Date":"2016-05-26","Rate":"400000"}},{"@attributes":{"Code":"DBL","Total":"200000"},"DayPrice":{"Date":"2016-05-26","Rate":"200000"}}]';

    console.log(priceJson);
    var priceObject = JSON.parse(priceJson);
    console.log(priceObject);

    if(priceObject.DayPrice.Rate)
        priceObject = [priceObject]; 
    else
        priceObject = priceObject;

    console.log(priceObject);
    var priceJson = JSON.stringify(priceObject);
    console.log(priceJson);

    var countRoomType = priceObject.length;
    for(var i=0; i<countRoomType; i++){ 
        console.log(priceObject[i].DayPrice.Date);
        console.log(priceObject[i].DayPrice.Rate);
    }


</script>

Demo (See in console) : https://jsfiddle.net/oscar11/wsqdha8w/1/

Variable priceJson has a dynamic value. The value can be one single instance of data or can be an array of data. If the value contains 1 data then I convert into a data array like this:

if(priceObject.DayPrice.Rate)
        priceObject = [priceObject]; 

But, in console there is the following error: TypeError: priceObject.DayPrice is undefined

Any solutions to solve my problem?