Assigning Values to JSON Objects in Javascript

Question

This is what I'm trying to build via JavaScript in dot or [ ] notation:

var shoppingCart = { 
        'item1' : {
            'description' : 'This is item #1',
            'price' : 10,
            'quantity' : 1,
            'shipping' : 0,
            'total' : 10
        }
    };

Now if 'item1' is the variable name itemName.

This works:
var shoppingCart = {};
shoppingCart[itemName] = itemName;
alert(shoppingCart.item1);

Which returns item1

But this doesn't work:
1 var shoppingCart = {};
2 shoppingCart[itemName]['description'] = 'This is Item #1';

JS just dies at line 2, why? and how do I assign the description value to 'description'?

I would do it like this:

var shoppingCart = { 
        itemName : {
            'description' : description,
            'price' : price,
            'quantity' : quantity,
            'shipping' : shipping,
            'total' : total
        }
    };

...but it makes the key literally itemName instead of item1.

SLaks · Accepted Answer · 2012-01-22 22:17:54Z

13

shoppingCart[itemName] doesn't exist.
You need to create it first:

var shoppingCart = {};
shoppingCart[itemName] = { };
shoppingCart[itemName].description = 'This is Item #1';

Or, better yet:

var shoppingCart = {};
shoppingCart[itemName] = { description: 'This is Item #1' };

edited Jan 22, 2012 at 22:17

answered Jan 22, 2012 at 22:05

SLaks

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2 Comments

Alex Wayne Over a year ago

Also shoppingCart[itemName]['description'] is equivalent to shoppingCart[itemName].description. You only need to access properties with [] when accessing them dynamically obj[propNameString] or when it contains illegal characters for dot notaton obj['some-prop-name']

phpKid Over a year ago

Yes thnx, that's what I read everywhere, but the key is that shoppingCart[itemName] = { }; I'm understanding objects more and more each day!

6502 · Accepted Answer · 2012-01-22 22:10:03Z

2

In javascript objects do not auto-create on member access; you have to create the object first:

var shoppingCart = {};
shoppingCart["item1"] = {}; // This creates the object
shoppingCart["item1"]["description"] = "This is item #1"; // add a member

Note you can of course also create the whole object at once with

shoppingCart[itemname] = { "description": description,
                           "price": price,
                           "quantity": quantity,
                           "shipping": shipping,
                           "total": total };

answered Jan 22, 2012 at 22:10

6502

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Comments

Ryan McGrath · Accepted Answer · 2012-01-22 22:05:55Z

1

It doesn't work because, in your second example, you're trying to index a blank object with a key that hasn't been set. The following will work...

var shoppingCart = {};
shoppingCart[itemName] = {};
shoppingCart[itemName]['description'] = '...';

Because now shoppingCart[itemName] is actually an object.

answered Jan 22, 2012 at 22:05

Ryan McGrath

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Comments

Renat Gatin · Accepted Answer · 2016-02-26 21:00:49Z

0

Just FYI, alternative solution:

var itemName = {};
itemName.description = 'This is Item #1';
var shoppingCart = {};
shoppingCart.itemName = itemName;

or just

var shoppingCart = {};
shoppingCart.itemName = { description: 'This is Item #1' };

answered Feb 26, 2016 at 21:00

Renat Gatin

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