Update an existing Hyperapp: https://codepen.io/okwolf/pen/ppdpgj?editors=0010

withUpdateApp.js

import { h, app } from "hyperapp"

// higher-order app function for update powers
const withUpdateApp = nextApp => {
  return (initialState, actionsTemplate, view, container) => {
    let currentView = view
    const enhancedActions = nextApp(
      initialState,
      {
        ...actionsTemplate,
        runAction: ({ action, data }) => state => {
          const result = action(data)
          return typeof result === "function"
            ? result(state, enhancedActions)
            : result
        },
        updateApp: ({ state = {}, actions = {}, view = currentView }) => {
          Object.keys(actions).forEach(name => {
            Object.assign(enhancedActions, {
              [name]: data =>
                enhancedActions.runAction({ action: actions[name], data })
            })
          })

          currentView = view

          return state
        }
      },
      (state, actions) => currentView(state, actions),
      container
    )
    return enhancedActions
  }
}

// Compose with app
const main = withUpdateApp(app)(state, actions, view, document.body)

// Use with updated state, actions, and/or view
main.updateApp({
  state: {
    // new state values from here will be merged in
  },
  actions: {
    // these actions will be added/overridden
  },
  view: {
    // optional new view function to use
  }
})

It is awesome. Thanks for your suggestions.