mergeWith()

Returns a copy of the collection with the remaining collections merged in, calling the merger function whenever an existing value is encountered.

A functional alternative to collection.mergeWith() which will also work with plain Objects and Arrays.

const { mergeWith } = require('immutable')
const original = { x: 123, y: 456 }
mergeWith(
  (oldVal, newVal) => oldVal + newVal,
  original,
  { y: 789, z: 'abc' }
) // { x: 123, y: 1245, z: 'abc' }
console.log(original) // { x: 123, y: 456 }run it