javascript - Jquery, checking if a value exists in array or not

I believe this question will be fairly easy for the ones who played
around with java script /
jquery.

var arr = new
            Array();


$.map(arr, function() {
 if (this.id
            == productID) {
 this.price = productPrice;
 }else {

            arr.push({id: productID, price: productPrice})

            }
}

I guess
the code above explains what I want in really simple way. I would imagine this $.map
would work like this but unfortunately I couldn't get results with
this.

What is the most simple and
elegant way to do this? Do I truly go through all array just to find if a key's value is
there or not?

Does Jquery has something like
isset($array['key'])?

EDIT

I
tried to use inArray but it keeps adding object to array even if there is a
match.

if ( $.inArray(productID,
            arr) > -1) {

 var number = $.inArray(productID, arr);

            orderInfo[number].price = parseFloat(productPrice);
}else {

            orderInfo.push({id:productID,
            price:parseFloat(productPrice)});
}

Answer

If you want to do it using
.map() or just want to know how it works you can do it like
this:

var
            added=false;

$.map(arr, function(elementOfArray, indexInArray)
            {
 if (elementOfArray.id == productID) {
 elementOfArray.price =
            productPrice;
 added = true;
 }
}
if (!added)
            {
 arr.push({id: productID, price:
            productPrice})
}

The
function handles each element separately. The .inArray()
proposed in other answers is probably the more efficient way to do
it.