JavaScript resolve reference from string and object

Question

is it possible to get a reference to an object with the object itself

obj

and the attributes in string form

'address.town.street'

so that at the end it resolves

obj.address.town.street

i could immageine smth like the eval() function.

any quick explanation why not to use it besides it is very slow? — alknows, Jan 22 '14 at 16:36
In general bad practice, teaches bad habits when there are good alternatives (like this one) — scrblnrd3, Jan 22 '14 at 16:37

score 3 · Accepted Answer · answered Jan 22 '14 at 16:26

3

Try

function getValue(obj, path) {
    return path.split(".").reduce(function(obj, name){ return obj[name]}, obj);
}

answered Jan 22 '14 at 16:26

Yury Tarabanko

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Just remember that if any of your intermediate objects, say `town` is null or undefined, this will throw an exception. If you have to add null-checking it gets significantly more complicated. – Scott Sauyet Jan 22 '14 at 17:05
@ScottSauyet 'more complicated'? Simple `return obj&&obj[name]` will almost do the trick. It will return false if path element was falsy. – Yury Tarabanko Jan 23 '14 at 06:28
@YuryTarabanko: You're absoultely right. It's not much more complicated. It won't necessarily return false, but that false-y value, but that's probably better anyway. This is so much simpler than approaches I've done (granted the problems were more complicated), but I thought the same null-checking issues would definitely rear their ugly heads here. Nicely done! – Scott Sauyet Jan 23 '14 at 14:40
This is one-liner which allows You to go one step further - it returns particular falsy value (in this case `null`): `path.split(".").reduce((obj, key) => obj && obj[key] || null, obj);` – jacqbus Mar 17 '23 at 07:59

score 0 · Answer 2 · answered Jan 22 '14 at 16:28

0

Do not use eval. Use this instead

Object.prototype.nestedByString=function(reference){
    var current=this;
    path=reference.split(".");
    for(var i=0;i<path.length;i++){
        current=current[path[i]];
    }
    return current;
}

Here is a demo

I suppose that if you're allergic to extending native prototypes, you can do this

function nestedByString(obj,reference){
        var current=obj;
        path=reference.split(".");
        for(var i=0;i<path.length;i++){
            current=current[path[i]];
        }
        return current;
}

answered Jan 22 '14 at 16:28

scrblnrd3

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Bad idea to spoil `Object.prototype`. – Yury Tarabanko Jan 22 '14 at 16:29
Why is it a bad idea? It was built into the language for a reason – scrblnrd3 Jan 22 '14 at 16:30
Well, cos another developers don't give a heck what this method is for. And this code will potencially break `for-in` loops without `.hasOwnProperty` checking. – Yury Tarabanko Jan 22 '14 at 16:32
this doesn't use a for in loop – scrblnrd3 Jan 22 '14 at 16:33
Sure but it will affect every `for-in` loop! :) – Yury Tarabanko Jan 22 '14 at 16:34
Why would it do that? How can I fix it? – scrblnrd3 Jan 22 '14 at 16:34
Coz your are extending Object.prototype and now every freaking object will inherit this method via prorototype chain. – Yury Tarabanko Jan 22 '14 at 16:35
I added an alternative without extending the prototype – scrblnrd3 Jan 22 '14 at 16:36
1

You can fix it in modern browsers by defining non-enumerable property. `Object.defineProperty(Object.prototype, 'nestedByString', {value: function(){/*blah*/}, enumerable: false})` – Yury Tarabanko Jan 22 '14 at 16:37
I find it somewhat amusing that this comment starts by repeating one of the modern so-called best practices about avoiding `eval` and then describes a solution that breaks another of them by updating `Object.prototype`. (Yes I see the alternate version as well.) It's not that I necessarily disagree, but I do find it amusing. – Scott Sauyet Jan 22 '14 at 17:12

JavaScript resolve reference from string and object

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