Question

Given a nested object like this:

var cars = {
    "bentley": {
        "suppliers": [
            {
            "location": "England",
            "name": "Sheffield Mines"}
        ]
        // ...
    }
};

and an array like this ["bentley", "suppliers", "0", "name"], is there an existing function that will pluck the deepest element, i.e. pluck_innards(cars, ['bentley', "suppliers", "0", "name"]) and that returns “Sheffield Mines”.

In other words, is there a function (which I will name deep_pluck) where

deep_pluck(cars, ['bentley', 'suppliers', '0', 'name']) 
         === cars['bentley']['suppliers']['0']['name']

It seems to me that this is simple, yet common enough, to have probably been done in one of the Javascript utility libraries such as jQuery or lo-dash/underscore – but I have not seen it.

My thought is something trivial, along the lines of:

function deep_pluck(array, identities) {
    var this_id = identities.shift();
    if (identities.length > 0) {
        return deep_pluck(array[this_id], identities);
    }
    return array[this_id];
}

Which I have posted on jsFiddle.

It would be helpful of course if the function were smart enough to identify when numerical indexes in arrays are needed. I am not sure offhand what other caveats may be a concern.

This is all a fairly long question for something I imagine has already been cleverly solved, but I thought to post this as I would interested in seeing what solutions are out there.

Answer 1

I don’t think you’ll have problems with Array indexes if you pass them as number 0.

Here’s alternative version of your function without recursion:

function deep_pluck(object, identities) {
    var result = object;
    for(var i = 0; i < identities.length; i++) {
        result = result[identities[i]];
    }
    return result;
}

Working example here: http://jsfiddle.net/AmH2w/1/