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>

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.