How to create a collection of items referencing collection itself

Question

I'm looking for a way of creating a collection of items, each of which would reference the collection itself.

Given:

const sources = [1, 2, 3];

Expected:

const results = [{value:1, items:[{value: 1, items:[{value: 1, items...}, ...]}]}]

Broken due to the fact that arrays are copied by value in js code:

const source = [1, 2, 3];
let result = [];

result = source.map(value => ({ value, items: result }));

I've tried a few things mainly around (()=> ...)(), but that gave me nothing. I managed to get it working with items being a function as opposed to value, which isn't exactly what I want.

Here's the best solution I found so far:

Code:

const source = [1, 2, 3];
let items = [];

items = source.map(value => () => ({ value, items }));

Usage:

items[1]().items[1]().value // 2
items[1]().items[2]().items[0]().value // 1

Where are 2 and 3 used? The sample looks like an endless collection. — briosheje, May 02 '19 at 09:57
@briosheje they are. every items should reference the entire collection. This will result in a recursive collection, correct. — JsCoder, May 02 '19 at 09:58
@JsCoder post the JavaScript that fails in returning said expected result. — zer00ne, May 02 '19 at 10:13
@JsCoder You are required to post something like a function -- something that doesn't work so that we can fix it. Your question is not a request to fix broken code that you are working on -- your question is a request for code without any work on your side. Post a [mcve] — zer00ne, May 02 '19 at 10:33

score 1 · Accepted Answer · answered May 02 '19 at 11:42

1

Self-references in object literals / initializers applies here. In your case, getters would be a good solution:

const result = [1, 2, 3].map(value => ({value, get items() { return result; }}));

answered May 02 '19 at 11:42

Bergi

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score 0 · Answer 2 · answered May 02 '19 at 09:58

0

That can't be done in one step. You have to create an array of objects first:

 const results = sources.map(value => ({ value }));

Then link back:

 results.forEach(result => result.items = results);

answered May 02 '19 at 09:58

Jonas Wilms

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I was thinking of using curry'ed constructors but I don't have much experience with currying - any value to be had by using it here? – JsCoder May 02 '19 at 10:01

How to create a collection of items referencing collection itself

2 Answers2