How to define a recursive object with a single expression?

Question

For example, given this object:

let foo = {foo:1};
let bar = {a:foo,b:foo};

We can define bar as a single expression by writing it as:

let bar = (($0)=>({a:$0={foo:1},b:$0}))()

However, given this object:

let o = {a:'perfect'};
o.circle = o;

Is it possible to recreate the structure of o with a single expression?

This won't work:

(($0)=>($0={a:"perfect",circle:$0}))()

Because circle is nested and $0 has been defined yet.

Would using Object.assign() be able to do what you want? I feel like it might. — Dylan LaCoursiere
– Dylan LaCoursiere, Commented Aug 18, 2017 at 2:32
({...$0={a:'perfect'},circle:$0}). Use Object.assign as necessary. I really don't see why you need this. — Andrew Li
– Andrew Li, Commented Aug 18, 2017 at 2:33
@AndrewLi That won't create a reference cycle but just lead to the same result as {a:'perfect',circle:{a:'perfect'}} — Bergi
– Bergi, Commented Aug 18, 2017 at 3:06
@Bergi Oh, I see. They want circle also in the circle property? — Andrew Li
– Andrew Li, Commented Aug 18, 2017 at 3:07
@AndrewLi Yes, I think so. Object.assign($0={a:'perfect'}, {circle:$0}) could do that. — Bergi
– Bergi, Commented Aug 18, 2017 at 3:14

Bergi · Accepted Answer · 2017-08-18 03:00:45Z

1

Unless you want to solve this with getter properties, an assignment is unavoidable.

There are all kinds of ways to do that, even within a single expression:

let o = (o = {a:'perfect'}).circle = o;

But I would recommend to focus on clarity and use an IIFE instead:

const o = (function(){
    const x = {a:'perfect'};
    x.circle = x;
    return x;
}());
// more like the first solution but without the mutable `o` variable:
const o = (x => x.circle = x)({a:'perfect'});

answered Aug 18, 2017 at 3:00

Bergi

671k162 gold badges1k silver badges1.5k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to define a recursive object with a single expression?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related