Populate second array in an object with values from its first array

Question

I have situation like this

const links = {
  ALLOWED1: [ 'some_path1' ],
  ALLOWED2: [ 'some_path2' ]
}

However I want to also allow paths from previous array on ALLOWED2, I've tried

const links = {
  ALLOWED1: [ 'some_path1' ],
  ALLOWED2: [ ...links['ALLOWED1'], 'some_path2' ]
}

But this is not valid as links will not defined yet. Of course I can populate it manually, but would rather find a more elegant solution.

@AlexandruSeverin Manually, this is for routing, however I would like to find a solution to get strings from previous array and move them into next one, that wouldn't be manual. — Ilja
– Ilja, Commented Dec 5, 2016 at 15:31

fet · Accepted Answer · 2016-12-05 16:07:20Z

2

You could do it with three lines instead

const links = {};
links.ALLOWED1 = [ 'some_path1' ];
links.ALLOWED2 = [ ...links['ALLOWED1'], 'some_path2' ];

console.log(links.ALLOWED2);

Remember, const only keeps the reference to the object constant, not the object's contents. For that you would need Object.defineProperty

If the contents of allowed1 and allowed2 ever change I might consider using a function to get them both. Like: links.all = () => [...links.ALLOWED1, ...links.ALLOWED2]. To me, that would read clearer in the code, unless it's really clear that allowed2 will always be a superset of allowed1.

edited Dec 5, 2016 at 16:07

answered Dec 5, 2016 at 15:30

fet

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1 Comment

fet Over a year ago

Oops, thank you. Wish stackoverflow had a syntax checker :)

Ori Drori · Accepted Answer · 2016-12-05 15:49:28Z

2

If you're not going to change ALLOWED2, you can convert it to a getter:

const links = {
  ALLOWED1: [ 'some_path1' ],
  get ALLOWED2() { return [ ...this['ALLOWED1'], 'some_path2' ] }
}

console.log(links.ALLOWED2);

answered Dec 5, 2016 at 15:49

Ori Drori

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Comments

user3297291 · Accepted Answer · 2016-12-05 15:43:56Z

0

An alternative, just because there are many ways to do this and it's mostly a matter of style :)

const links = (() => {
  const ALLOWED1 = ["some_path1"],
        ALLOWED2 = [...ALLOWED1, "some_path2"];
               
  return { ALLOWED1, ALLOWED2 };
})();

console.log(links);

answered Dec 5, 2016 at 15:43

user3297291

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