How to create an immutable map from .map() JS

Question

So I have a function like this

myNewMap = oldMap.map((check) => {
     if (check.get('_id') === against.get('_id')) return check;
});

The only problem is myNewMap is the same size as the oldMap (which makes sense), but is there a way to stop this, or do I need a different approach?

Luka Jacobowitz · Accepted Answer · 2016-03-09 16:32:39Z

3

I think you want filter

myNewMap = oldMap.filter((check) => {
   return check.get('_id') === against.get('_id');
});

Or even shorter:

myNewMap = oldMap.filter(check => check.get('_id') === against.get('_id'));

This will return a new Map with only the values that meet the predicate.

answered Mar 9, 2016 at 16:27

Luka Jacobowitz

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Comments

andre mcgruder · Accepted Answer · 2016-03-09 17:18:06Z

0

After you map over the array you can do

Object.seal( yourMappedArrayObject );

That will make that object then immutable.

answered Mar 9, 2016 at 17:18

andre mcgruder

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I don't think that's what he was asking.