SPA can load custom scripts. We do not have control of the SPA otherwise. These files can isolate recurring code so it does not persist from page to page

isolateEventListener.js

(function() {

// Isolate Event Listener so it is safe to use
// current URL is checked each time the event listener is activated
// if a different page is loaded, the event will destroy itself the next time it is active

// In this demo, we are able to completely isolate this behavior inside
// an abstraction called createIsolatedEvent, which is fully reusable


  // createIsolatedEvent abstraction
  function createIsolatedEvent (element, type, callback) {
    function currentPage () { return window.location.pathname }
    var startingPage = currentPage()

    function isolatedCallback(event) {
      var hasChangedPages = (startingPage !== currentPage())

      if (hasChangedPages) {
        element.removeEventListener(type, isolatedCallback)
        return  
      }
      return callback(event)
    }
    element.addEventListener(type, isolatedCallback)
  }

  // Example Usage
  function handleClick (event) {
    console.log(event.target)
  }

  createIsolatedEvent(window, 'click', handleClick) // abstraction of window.addEventListener('click', handleClick)

})()

isolateInterval.js

(function() {

  // setIsolatedInterval
  // an alternative to the isolateInterval code
  // which wraps all of the interval functionality in an abstraction
  
  // setIsolatedInterval can be used as an alternative to setInterval
  // with all the termination logic built inside
  

  function setIsolatedInterval (callback, milliseconds) {
    function currentPage () { return window.location.pathname }
    var startingPage = currentPage()
    var interval

    function isolatedCallback () {
      var hasChangedPages = (startingPage !== currentPage())
  
      if (hasChangedPages) {
        clearInterval(interval)
        return
      }
      return callback()
    }
  
    interval = setInterval(isolatedCallback, milliseconds)
    return interval
  }
  
  // Example Usage
  function doSomethingRepeatedly () {
    console.log('Running isolated interval')
  }
 
  setIsolatedInterval(doSomethingRepeatedly, 1000) // abstraction of setInterval(doSomethingRepeatedly, 1000)

})()