Cannot assign new values to object in Javascript

I'm currently trying to take two objects of objects, where the second one has updated values, and merge the updated values into the first one. I wrote a function to do this but i'm unable to update the values within my AnimatedDataWrapper. However if I run it outside of the AnimatedDataWrapper it works fine..

import React, { Component } from 'react'
import PropTypes from 'prop-types'
import * as d3 from 'd3'

const mapNewStateToOldState = (oldState, newState) => {
  Object.keys(oldState).forEach((key) => {
    Object.assign(oldState[key], newState[key])
  })
  return oldState
}

// const mapNewStateToOldState = (oldState, newState) =>
//  Object.keys(oldState).map(key => Object.assign(oldState[key], newState[key]))

const obj = { 0: { data: 1 } }
const newObj = { 0: { data: 2 } }

console.log(mapNewStateToOldState(obj, newObj)) // THIS WORKS
console.log(obj) // THIS WORKS

const AnimatedDataWrapper = (dataProp, transitionDuration = 300) => ComposedComponent =>
  class extends Component {
    constructor(props) {
      super(props)
      const data = this.props[dataProp]
      this.state = Object.keys(data)
        .map(label => ({ [label]: data[label] }))
        .reduce((prev, curr) => ({ ...prev, ...curr }), {})
    }

    componentWillReceiveProps(nextProps) {
      const data = this.props[dataProp]
      console.log(data)
      const nextData = nextProps[dataProp]
      const dataKeys = this.props.dataKeys
      const dataUnchanged = Object.keys(data)
        .map(label => data[label] === nextData[label])
        .reduce((prev, curr) => prev && curr)
      if (dataUnchanged) {
        return
      }
      d3.select(this).transition().tween('attr.scale', null)
      d3
        .select(this)
        .transition()
        .duration(transitionDuration)
        .ease(d3.easeLinear)
        .tween('attr.scale', () => {
          const barInterpolators = data.map((...args) => {
            const index = args[1]
            return dataKeys.map((key) => {
              const interpolator = d3.interpolateNumber(
                this.state[index][key],
                nextData[index][key],
              )
              return { key, interpolator }
            })
          })
          return (t) => {
            const newState = barInterpolators
              .map(bar =>
                bar
                  .map(({ key, interpolator }) => ({ [key]: interpolator(t) }))
                  .reduce((result, currentObject) => {
                    Object.keys(currentObject).map((key) => {
                      if (Object.prototype.hasOwnProperty.call(currentObject, key)) {
                        result[key] = currentObject[key]
                      }
                      return null
                    })
                    return result
                  }, {}),
              )
              .reduce((newObject, value, index) => {
                newObject[index] = value
                return newObject
              }, {})
            const oldState = this.state
            console.log(`OLD STATE = ${JSON.stringify(oldState)}`)
            console.log(`NEW STATE = ${JSON.stringify(newState)}`)
            const updatedState = mapNewStateToOldState(oldState, newState) // THIS DOES NOT WORK
            console.log(`UPDATED STATE = ${JSON.stringify(updatedState)}`)
            this.setState(updatedState)
          }
        })
    }

    render() {
      const { props, state } = this
      const newData = Object.keys(state).map(val => state[val])
      const newDataProps = { ...{ data: newData } }
      const newProps = { ...props, ...newDataProps }
      return <ComposedComponent {...newProps} />
    }
  }

AnimatedDataWrapper.PropType = {
  dataProp: PropTypes.string.isRequired,
  transitionDuration: PropTypes.number,
  dataKeys: PropTypes.instanceOf(Array).isRequired,
  maxSurf: PropTypes.number.isRequired,
}

export default AnimatedDataWrapper

Here is what the objects i'm passing into the function mapNewStateToOldState (oldState, newState) look like. And what the output updatedState looks like.

It seems like maybe it would be a scoping issue? But i can't seem to figure out what is going on. I tried manually merging it with no luck either.