registerProtocolHandler.html

This code won't run - just trying to get the idea across of how we might replace registerProtocolHandler, but only if register and registee both agree to use the replacement.


Page that wants to register:
<iframe class="hidden" src="http://you.github.io/registerProtocolHandler/" id="registerProtocolHandler"></iframe>
<script>
document.getElementById("registerProtocolHandler").contentWindow.postMessage({
    operation: "setRegistration", 
    scheme: "web+action",
    handler: "http://me.com/?url=%s"
}, "http://you.github.io/");
</script>


Page that wants to read a registration:
<iframe class="hidden" src="http://you.github.io/registerProtocolHandler/" id="registerProtocolHandler"></iframe>
<script>
addEventListener("message", function (eventArg) {
    // received registration info for 'web+action'
});
document.getElementById("registerProtocolHandler").contentWindow.postMessage({
  operation: "getRegistration"
  scheme: "web+action"
}, "http://you.github.io/");
</script>


The http://you.github.io/registerProtocolHandler/index.html page:
<script>
addEventListener("message", function (eventArg) {
    switch (eventArg.data.operation) {
    case "setRegistration":
        if (confirm("Let " + eventArg.data.handler + " handle " + eventArg.data.scheme + "?")) {
            localStorage["registration"] = localStorage["registration"] || {};
            localStorage["registration"][eventArg.data.scheme] = eventArg.data.handler;
        }
        break;
    case "getRegistration":
        eventArg.source.postMessage({
            scheme: eventArg.data.scheme, 
            handler: (localStorage["registration"] || {})[eventArg.data.scheme]
        }, eventArg.origin);
        break;
    }
});
</script>

@david-risney Apart from that – how would we prevent that anyone else calls "setRegistration".
The most important point in the spec. here is the "native ui baked in the browser" to ask the user in front of Edge...

Just for my example I have a confirm call to ask the user if they want to allow registration. For the real thing you'd probably want to open a new window and present better, richer UX.