Computed destructuring of nested Objects

Question

It's convenient to extract properties from Objects by destructuring:

let o = {id: "100", name: "Jane Doe", address: {id:1, city:"Fargo"}},
 key = "address";

let {address: {id: id}} = o; // 1

Destructuring patterns can be computed as well:

let {[key]: {city: city}} = o; // Fargo

But it seems apparently not possible to extract properties of nested objects dynamically:

key = "address.city";
({[key]: city} = o); // undefined

Is it possible to destructure nested Objects with computed patterns?

score 4 · Accepted Answer · edited May 23 '17 at 12:31

4

No, this is not possible. Destructuring is only for objects whose structure you know about. You could of course do

var keys = ["address", "city"];
var {[keys[0]]: {[keys[1]]: city}} = o;

but not for arbitrarily nested objects. You'll have to use a recursive function for that which walks the property path. See the question Convert JavaScript string in dot notation into an object reference and many others for that.

edited May 23 '17 at 12:31

Community

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answered May 29 '16 at 15:38

Bergi

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I know that reduce or recursion are suitable tools for this issue. I've just wondered if destructuring provides an alternative way. Thanks! – May 29 '16 at 15:53

score 2 · Answer 2 · 2016-05-29T18:07:47.090

2

No, it's not possible. JavaScript has no concept of these "object paths" like "p1.p2" that people seem to be so enamored of, whether it be in the context of destructuring or anywhere else.

edited May 29 '16 at 18:07

answered May 29 '16 at 15:35

score -1 · Answer 3 · edited May 23 '17 at 11:53

I had written a standard reusable Object method to access nested properties dynamically. You can use this on any object to access your nested value. It's called Object.prototype.getNestedValue()

Object.prototype.getNestedValue = function(...a) {
  return a.length > 1 ? (this[a[0]] !== void 0 && this[a[0]].getNestedValue(...a.slice(1))) : this[a[0]];
};

So once you have this it's very easy. It will take dynamic arguments for the nested properties. If they are string type they are object properties if number type then they are array indices. Once you have this, your job becomes very easy. Let's see..

Object.prototype.getNestedValue = function(...a) {
  return a.length > 1 ? (this[a[0]] !== void 0 && this[a[0]].getNestedValue(...a.slice(1))) : this[a[0]];
};

let o = {id: "100", name: "Jane Doe", address: {id:1, city:"Fargo"}},
props = ["address","city"],
    v = o.getNestedValue(...props);
console.log(v);
// you can also pass static parameters of course...
v = o.getNestedValue("address","city");
console.log(v);

You can see getNestedValue() and it's twin setNestedValue() working at https://stackoverflow.com/a/37331868/4543207

[Don't extend `Object.prototype` like that](http://stackoverflow.com/q/13296340/1048572). — Bergi, May 29 '16 at 22:07
@Bergi Thanks for pointing this out. It's something really worthwhile to pay attention at production code. — Redu, May 29 '16 at 22:10

Computed destructuring of nested Objects

3 Answers3