infinte_curry.js

const update = (obj) => {
  const next = (...args) => {
    return x => {
      if (
        typeof x === 'object' 
        // && x.constructor.name.includes('Event')
        ) {
        let node = obj
        for (let i = 0; i < args.length - 1 ; i++) {
          node = node[args[i]]
        }
        node[args[args.length - 1]] = x.target.value
      }
      return next(...args, x)
    }
  }
  return next
}

const Obj = {
  reward: {
    xp: 12
  }
}
const event = {
  target: {
    value: 13
  }
}
const updater = update(Obj)
updater('reward')('xp')(event)

console.log(Obj)