Provide a simple solution to create big portion of state when given some small portions

StateBuilderIdea.js

sb = new StateBuilder()

state = sb.setQuery({})
  .setConverstion.setMultipleChoiceQuestion({})
  .setConverstion.setFreeTextQuestion({})
  .build()

class StateBuilder extends GenericStateBuilder {
  constructor(args) {
    super(args)
  }
  get setConversation() {
    // Singleton
    if (!this._conversationStateBuilder) {
      this._conversationStateBuilder = new ConversationStateBuilder(this.rootStateBuilder)
      this.state.consersation = this._conversationStateBuilder
    }
    return this._conversationStateBuilder
  }
  setQuery(state) {
    this.state.query = state
    return this.rootStateBuilder
  }
}

class GenericStateBuilder {
  constructor(that = this) {
    this.rootStateBuilder = that
    this.state = {}
  }
  build() {
    const getState = () => Object.entries(this.state)
      .reduce((acc, [key, value]) => {
        if (value instanceof GenericStateBuilder) {
          acc[key] = value.build();
        } else if (value !== undefined) {
          acc[key] = value
        }
        return acc
      }, {})
    return getState()
  }
}

class ConversationStateBuilder extends GenericStateBuilder {
  constructor(args) {
    super(args)
  }
  setMultipleChoiceQuestion(state) {
    this.state.questions = state
    return this.rootStateBuilder
  }
  setFreeTextQuestion(state) {
    this.state.freeText = state
    return this.rootStateBuilder
  }
}