Question

I am using jQuery, Backbone (and underscore) and RequireJS.

I have this code:

var products = _.map(items, function(item) {
    return new ProductModel({
        title: item.product.title,
        description: item.product.description,
        link: item.product.link,
        'image-src': item.product.images[0].link,
        'image-height': item.product.images[0].height,
        'image-width': item.product.images[0].width
    });
});

Unfortunately, everything might be null. By everything I mean that item, item.product, item.product.images, item.product.images[0] and so on might be nulls.

I am looking for something like “coalesce” that:

1. will know how to handle nulls and will not throw exceptions for item.product if item is null.
2. will allow me to provide a default value if there was a null.

Is there anything like that?

Answer 1

You can use boolean && and rely on short-circuiting:

...
'image_src': item && item.product && item.product.images && item.product.images[0] && item.product.images[0].link,
'image_height': item && item.product && item.product.images && item.product.images[0] && item.product.images[0].height,
...

More likely, you don’t want to perform the same test across so many lines. I would store your return value with its various attributes set to some sane default and then conditionally add the real values if your item.product.images[0] is non-null:

var returnObject = { /* default values here */ }, product, image;

if (product = item && item.product) {
    returnObject.title = product.title,
    returnObject.description = product.description,
    returnObject.link = product.link
};

if (image = product && product.images && product.images[0]) {
    returnObject['image-src'] = image.link;
    returnObject['image-height'] = image.height;
    returnObject['image-width'] = image.width;
}

return returnObject;