Getting an Objects nested value from an array of nested properties

Question

I have a situation where I need to zip two Objects together retaining both of the values. I can iterate through both the objects and build an array of all the keys.

    var traverse = function (obj, chain) {

        for (var prop in obj) {
            if (obj.hasOwnProperty(prop)) {

                var tempChain = [].concat(chain || []);
                tempChain.push(prop);

                if (typeof obj[prop] === 'object') {
                    traverse(obj[prop], tempChain);
                }
                console.log(tempChain);
            }
        }
    };

Passing in the following:

    traverse({
        'a': {
            'b': 'hello world',
            'b1': 'hello world 1',
            'c': {
                'd': 'dello'
            }
        }
    })

Will return me:

[a]
[a,b]
[a,b1]
[a,c]
[a, c, d]

So I now have an array of nested properties in an object. How can I access essentially obj[[a,c,d]]? I know I can solve the problem through eval but I can't trust the content.

eval('window.' + ['a','c','d'].join('.'));

If I can loop through that array and check to see if the property exists in both of them, then build a new object of the combined 'zipped' values.

window !== obj, that wouldn't work anyway. But yes, you can use a simple loop. — Bergi
– Bergi, Commented Oct 4, 2013 at 12:12
Check any of these duplicates - just omit the .split(".") as you have an array already — Bergi
– Bergi, Commented Oct 4, 2013 at 12:19
I think this is some kind of XY problem. What exactly is your zip supposed to do, and why would you need property chains for that? — Bergi
– Bergi, Commented Oct 4, 2013 at 14:35

plalx · Accepted Answer · 2013-10-04 14:13:43Z

1

Perhaps something like this?

function getValueAt(obj, keyPathArray) {
    var emptyObj = {};

    return keyPathArray.reduce(function (o, key) {
        return (o || emptyObj)[key];
    }, obj);
}

Then you can use it like:

var o = { a: { c: { d: 1 } } };

getValueAt(o, ['a', 'c', 'd']); //1

However it's not efficient for non-existing properties, since it will not short-circuit. Here's another approach without using reduce:

function getValueAt(o, keyPathArray) {
    var i = 0, 
        len = keyPathArray.length;

    while (o != null && i < len) o = o[keyPathArray[i++]];

    return o;    
}

edited Oct 4, 2013 at 14:13

answered Oct 4, 2013 at 12:04

plalx

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4 Comments

Bergi Over a year ago

Why not simply while (o!=null && i<l) o = o[keyPathArray[i++]];? Currently you will always return undefined when i exceeds the length, and it will fail when o becomes null somewhere.

dtsn Over a year ago

I've tried using both your solutions however the function returns the value and I want the object pointing to the value. To give a better explanation heres some working code which are using evals. jsbin.com/EHeFayu/7

plalx Over a year ago

@Bergi, Yeah, somehow I haven't tought that the last value could be an object and that typeof null was 'object'. Silly mistakes. Fixed.

plalx Over a year ago

@dtsn, I cannot access jsbin right now, however I believe you could just ignore the last element in the array and it will return the object holding that property. var keyPath = ['a', 'b', 'c']; keyPath = keyPath.slice(0, keyPath.length - 1); getValueAt(o, keyPath); Obviously you have to hold a reference to the root object.

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