blockscout/apps/block_scout_web/assets/js/pages/block.js

import $ from 'jquery'
import humps from 'humps'
import socket from '../socket'
import router from '../router'
import { updateAllAges } from '../lib/from_now'
import { initRedux } from '../utils'

export const initialState = {
  beyondPageOne: null,
  channelDisconnected: false,
  newBlock: null
}

export function reducer (state = initialState, action) {
  switch (action.type) {
    case 'PAGE_LOAD': {
      return Object.assign({}, state, {
        beyondPageOne: !!action.blockNumber
      })
    }
    case 'CHANNEL_DISCONNECTED': {
      if (state.beyondPageOne) return state

      return Object.assign({}, state, {
        channelDisconnected: true
      })
    }
    case 'RECEIVED_NEW_BLOCK': {
      if (state.channelDisconnected || state.beyondPageOne) return state

      return Object.assign({}, state, {
        newBlock: action.msg.blockHtml
      })
    }
    default:
      return state
  }
}

router.when('/blocks', { exactPathMatch: true }).then(({ blockNumber }) => initRedux(reducer, {
  main (store) {
    const blocksChannel = socket.channel(`blocks:new_block`, {})
    store.dispatch({ type: 'PAGE_LOAD', blockNumber })
    blocksChannel.join()
    blocksChannel.onError(() => store.dispatch({ type: 'CHANNEL_DISCONNECTED' }))
    blocksChannel.on('new_block', (msg) =>
      store.dispatch({ type: 'RECEIVED_NEW_BLOCK', msg: humps.camelizeKeys(msg) })
    )
  },
  render (state, oldState) {
    const $channelDisconnected = $('[data-selector="channel-disconnected-message"]')
    const $blocksList = $('[data-selector="blocks-list"]')

    if (state.channelDisconnected) $channelDisconnected.show()
    if (oldState.newBlock !== state.newBlock) {
      $blocksList.prepend(state.newBlock)
      updateAllAges()
    }
  }
}))