native JS async-iterator event stream

1.js

async function main() {
   var btn = document.getElementById("my-button");
  
   // eventStream here is a native JS async iterator
   var eventStream = onEvent(btn)("click");
  
   // this is the key thing: we can use a `for-await..of` loop
   // to consume the async-iterator
   for await (let evt of eventStream) {
      console.log("click!");
   }
}

main();

2.js

var onEvent = el => evtName => {
   var { pr, next } = getDeferred();

   el.addEventListener(evtName,handler,false);

   return eventStream();

   // ******************   

   async function *eventStream(){
      while (true) {
         yield pr;
      }
   }

   function handler(evt) {
      var f = next;
      ({ pr, next } = getDeferred());
      f(evt);
   }

   function getDeferred() {
      var next;
      var pr = new Promise(res => next = res);
      return { pr, next };
   }
};