Like mergeDeep(), but when two non-collections or incompatible
collections are encountered at the same key, it uses the merger function
to determine the resulting value. Collections are considered incompatible
if they fall into separate categories between keyed, indexed, and set-like.
mergeDeepWith<C>(merger: (oldVal: unknown, newVal: unknown, key: unknown) => unknown,
collection: C,
...collections: Array<Iterable<unknown> | Iterable<[unknown, unknown]> | {[key: string]: unknown}>): C
A functional alternative to collection.mergeDeepWith() which will also
work with plain Objects and Arrays.
const { mergeDeepWith } = require('immutable')
const original = { x: { y: 123 }}
mergeDeepWith(
(oldVal, newVal) => oldVal + newVal,
original,
{ x: { y: 456 }}
) // { x: { y: 579 }}
console.log(original) // { x: { y: 123 }}run it