Is data returned by JavaScript (ES6) array.filter() immutable? It depends.
If the original array contains “primitive” values (eg. strings, numbers and boolean) then a new array with “copies” of the values is returned in the filtered array. Changing data in the returned array will not affect the original array or its data.
If the original array contains objects then the a new array is still returned from .filter() but each element still references the object in the original array. Changing data in either the original or returned array will affect the data in both array because it’s the same piece of data being referenced by both arrays.
I have a Pen at https://codepen.io/jsnelders/pen/jOPeXXw demonstrating both situations.
See the Pen
Is data returned by JavaScript (ES6) array.filter() immutable? by Jason (@jsnelders)
on CodePen.