force-sendBeacon-polyfill-async.js

!(function(){
  if (typeof navigator.sendBeacon !== 'function') return
  if (/\[native code\]/.test(Function.prototype.toString.call(navigator.sendBeacon))) return

  var orig_sendBeacon = navigator.sendBeacon
  
  window.addEventListener('unload', function() {
    navigator.sendBeacon = orig_sendBeacon
  })
  
  navigator.sendBeacon = function() {
    var orig_open = XMLHttpRequest.prototype.open
    XMLHttpRequest.prototype.open = function() {
      if (arguments.length < 3)
        return orig_open.apply(this, arguments)

      var args = Array.prototype.slice.call(arguments)
      args[2] = true
      return orig_open.apply(this, args)
    }
    
    var returnValue, didThrow = false, e
    try {
      returnValue = orig_sendBeacon.apply(this, arguments)
    } catch(_e) {
      didThrow = true
      e = _e
    }
    XMLHttpRequest.prototype.open = orig_open
    if (didThrow) {
      throw e
    }
    return returnValue
  }
})()