Question

We’re using jQuery on a less UI-intensive project whereas we have been using ExtJS on other projects. Regardless, I’m curious if any of the prevalent libraries such as ExtJS, jQuery, or others, provide a utility for “pruning” objects? By which I mean, deleting keys if they don’t contain values.

I’ve devised my own (naive) implementation as follows, so its no biggie. Still though just curious as I believe this could be generally useful. I’ve googled for “jquery prune object” but no results seem worth investigating though of course I could be wrong 😉

function pruneObj(obj) {
    var empty = [];
    for (var attr in obj) {
        if (!obj[attr]) {
            empty.push(attr); //rather than trying to delete the element in place
        }
    }
    for (var i=0, n=empty.length; i<n; i++) {
        delete(obj[empty[i]]);
    }
    return obj;
}

Answer 1

So:

var obj = { hasFoo: false, count: 0 }

would (after a call to prunObj(obj)) be just {}?

I don’t think any library out there would make the assumption of what values to deem “empty”. It’s too destructive/mutative a function to include as part of a standard set of utility functions.

Many libraries or browsers include a facility to filter out items from arrays that don’t meet a certain criteria. Eg filter:

list.filter(function(item){
    return !item.foo
})

will filter out items in list that have a “falsey” value in the foo property.

Edit:

On further thought, undefined seems to be considered “empty” by both jQuery and Prototype. jQuery’s extend function can do what I think you’re aiming for with undefined, albeit with a slightly different syntax and without mutating the passed argument:

A = { hasFoo: false, count: 0, foo: null, bar: undefined };
B = jQuery.extend({}, A); // B = { hasFoo: false, count: 0, foo: null }

Swap "jQuery" with "Object" for the Prototype equivalent.