Inside the callback in Array.prototype.map, reference the new array

Question

Array.prototype.map() returns a new array. I want to reference this new array inside the callback function passed as the argument to Array.prototype.map(). Can I do that?

Example

someArray.map(function(item, idx, arr) {
    return { theCreatedArray: xyz };
});

What should xyz be?

EDIT [Context]

Why do I want this? The object I create in the callback is of a type that relies on having a reference to the array that is referencing the object. I can't refactor this requirement so easily. I would rather satisfy it.

"Can I do that?" No. The new array is returned by map, there is no way to access it during the process. — Felix Kling
– Felix Kling, Commented Jan 28, 2015 at 15:40
It helps people to provide more useful answers and guidance if you explain a little bit about the context of your question. What is it that you're trying to do? — Pointy
– Pointy, Commented Jan 28, 2015 at 15:42

Pointy · Accepted Answer · 2015-01-28 15:40:55Z

4

You can't do it with .map(), but you can do it with .reduce():

someArray.reduce(function(rv, item, idx) {
  // rv is the return value, in this case your array
  rv.push({whatever: rv});
  return rv;
}, []);

answered Jan 28, 2015 at 15:40

Pointy

415k62 gold badges600 silver badges631 bronze badges

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

3 Comments

ssube Over a year ago

Should rv.push use {whatever: item} rather than rv? This creates an infinitely-nested list (run from my chrome console).

Pointy Over a year ago

@ssube well it's just an example; the point is that rv is a reference to the array. (It's not necessarily a bad thing to have a data structure with cycles anyway.)

David Groomes Over a year ago

Excellent. Array.prototype.reduce is more capable than map, but is a more conceptually difficult function. I'll use this.

Collectives™ on Stack Overflow

Inside the callback in Array.prototype.map, reference the new array

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related