!7

html {
  if (eq(uri, "/worker.js"))
    ret [[
      postMessage("WORKING!");
      var startTime = new Date();
      var i = 0;
      while (true) {
        i = i+1;
        if ((i % 1000000) == 0) {
          var ms = new Date()-startTime;
          var mips = (i/ms/1000).toFixed(2);
          postMessage("Counted to: " + i + " in " + ms + " ms ("
            + mips + " million steps/s)");
        }
      }
    ]];
    
  ret htitle("Web Worker Test")
    + hbody(
      p(hfulltag("output", "", id := "result1"))
    + p(hfulltag("output", "", id := "result2"))
    + p(hbutton("Restart Worker", onClick := "restart()"))
  + hjavascript([[
    var workers = [];
    
    function restart() {
      for (w of workers) { w.terminate(); }
      workers = [];
      go();
    }
    
    function go() {
      for (i = 1; i <= $WORKERS; i++) go1(i);
    }
     
    function go1(i) { 
      var res = document.getElementById("result" + i);
      if (typeof(Worker) === "undefined") {
        res.innerHTML = "Sorry, your browser does not support Web Workers...";
        return;
      }
      res.innerHTML = "Making web worker";
      var worker = new Worker($LINK);
      worker.onmessage = function(event) {
        res.innerHTML = event.data;
      };
      workers.push(worker);
    }
  ]]).replace("$LINK", jsQuote(relativeRawBotLink(programID(), "worker.js"))), onLoad := "go()")
    .replace("$WORKERS", str(2));
}

Began life as a copy of #1013783