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HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.4.0/Rx.js"></script>

JavaScript

const gates$ = Rx.Observable.interval(2000)
													 .map(_ => Math.random() >= 0.5)
													 .map(x => ({gates: x}))
													 .share()
                                                 
const data$ = Rx.Observable.interval(500)
													 .map(_ => "data"+ _)
													 .map(x => ({data: x}))                           
                           .share()

const out$ = Rx.Observable.merge(gates$, data$).scan((acc, val) => {
  if (acc.controlState === 'passthrough'){
    if (Object.keys(val).includes('data')) {
      return {
        controlState : 'passthrough',
        bufferedData : [],
        out : val.data
      }
    }
    if (Object.keys(val).includes('gates')) {
      if (val.gates) {
        // gates passing from true to true -> no changes to perform
        return {
        controlState : 'passthrough',
        bufferedData : [],
        out : null
        }
      } else {
        // gates passing from true to false, switch control state
        return {
        controlState : 'buffered',
        bufferedData : [],
        out : null        
        }
      }      
    }
  }
  if (acc.controlState === 'buffered'){
    if (Object.keys(val).includes('data')) {
      return {
        controlState : 'buffered',
        bufferedData : (acc.bufferedData.push(val.data), acc.bufferedData),
        out : null              
      }
    }
    if (Object.keys(val).includes('gates')) {
      if (val.gates) {
        // gates from false to true -> switch control state and pass the buffered data
        return {
          controlState : 'passthrough',
          bufferedData : [],
          out : acc.bufferedData              
        }
      } else {
        // gates from false to false -> nothing to do
        return {
          controlState : 'buffered',
          bufferedData : acc.bufferedData,
          out : null                    
        }
      }
    }
  }
}, {controlState : 'passthrough', bufferedData : [], out:null})
.filter(x =>...