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bytheway.js
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bytheway.js
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(function (window) {
var currentTime = Date.now || function () { return new Date().getTime(); }
var myId = currentTime() + "-" + Math.random();
var messengers = {};
window.ByTheWay = function (localStorageKey, receiveOwn) {
var k = "m_" + localStorageKey;
var result = messengers[k];
if (!result) {
messengers[k] = result = makeMessenger(localStorageKey);
}
return {
broadcast: result.broadcast,
unicast: result.unicast,
onReceive: function (callback) {
return result.onReceive(callback, receiveOwn);
},
request: function (message, callback, recipient, timeoutMs) {
return result.request(message, callback, recipient, timeoutMs, receiveOwn);
},
id: result.id
};
}
function regexEscape(s) {
return s.replace(/[$^.+*\\[\]()?|{}]/g, "\\$&");
}
// the postMessage prefix ends with an exclamation point, so we want to
// prevent that character from being part of the prefix itself.
function postMessageEscape(s) {
return s.replace(/%/g, "%%").replace(/!/g, "%-");
}
var postMessagePrefix = "bytheway-self-" + myId + "-";
var localNotifiers;
function ensurePostMessageListener() {
if (localNotifiers)
return;
localNotifiers = {};
var messagePrefixRe = new RegExp("^" + postMessagePrefix + "([^!]*)!(.*)$"); // the prefix contains no regex-active characters, so no need for escaping
window.addEventListener("message", function (evt) {
if (evt.source !== window)
return;
evt.data.replace(messagePrefixRe, function (wholeMatch, escapedLocalStorageKey, serializedEnvelope) {
var notifier = localNotifiers["m_" + escapedLocalStorageKey];
if (notifier)
notifier(JSON.parse(serializedEnvelope));
});
}, false)
}
var storageNotifiers;
function ensureStorageListener() {
if (storageNotifiers || ! window.addEventListener)
return;
storageNotifiers = {};
window.addEventListener("storage", function onStorage(evt) {
var notifier = storageNotifiers["m_" + evt.key];
if (!notifier)
return;
if (!evt.newValue)
return;
try {
var envelope = JSON.parse(evt.newValue);
} catch (ex) {
return;
}
if (envelope.sender === myId)
return;
notifier(envelope);
});
}
function makeMessenger(localStorageKey) {
var counter = 0;
var externalListeners = [];
var ownListeners = [];
var pendingRequests = {};
function makeEnvelope(message) {
var result = {
sender: myId,
time: currentTime(),
id: counter,
message: message
};
counter++;
return result;
}
var notifySelfAsync;
// In non-foreground tabs, some browsers will delay setTimeouts by quite a bit,
// but message events are passed immediately.
if (window.postMessage && window.addEventListener) {
ensurePostMessageListener();
var escaped = postMessageEscape(localStorageKey);
var channelPrefix = postMessagePrefix + escaped + "!";
localNotifiers["m_" + escaped] = function (envelope) {
notifyListeners(envelope, ownListeners)
}
notifySelfAsync = function (serialized) {
window.postMessage(channelPrefix + serialized, "*");
}
} else {
notifySelfAsync = function (serialized) {
setTimeout(function () {
notifyListeners(JSON.parse(serialized), ownListeners);
}, 0);
}
}
ensureStorageListener();
storageNotifiers["m_" + localStorageKey] = function (envelope) {
notifyListeners(envelope, externalListeners);
}
function send(envelope) {
var serialized = JSON.stringify(envelope);
try {
localStorage.setItem(localStorageKey, serialized);
} catch (ex) {}
if (ownListeners.length) {
notifySelfAsync(serialized);
}
}
function broadcast(message) {
send(makeEnvelope(message));
}
function unicast(message, recipient) {
var envelope = makeEnvelope(message);
envelope.recipient = recipient;
send(envelope);
}
function request(message, callback, recipient, timeoutMs, receiveOwn) {
var envelope = makeEnvelope(message);
if (recipient)
envelope.recipient = recipient;
envelope.rsvp = true;
pendingRequests[envelope.id] = [];
setTimeout(function () {
var responses = pendingRequests[envelope.id];
delete pendingRequests[envelope.id];
var messages = [];
var envelopes = [];
for (var i = 0; i < responses.length; i++) {
if (receiveOwn || responses[i].sender !== myId) {
messages.push(responses[i].message);
envelopes.push(responses[i]);
}
}
callback(messages, envelopes);
}, timeoutMs || 100);
send(envelope);
}
function responderFor(envelope) {
return function (responseMsg) {
var responseEnv = makeEnvelope(responseMsg);
responseEnv.recipient = envelope.sender;
responseEnv.inResponseTo = envelope.id;
send(responseEnv);
}
}
function onReceive(callback, receiveOwn) {
externalListeners.push(callback);
if (receiveOwn)
ownListeners.push(callback);
}
function notifyListeners(envelope, listenersArray) {
if ("recipient" in envelope) {
if (envelope.recipient !== myId)
return;
if ("inResponseTo" in envelope) {
var pr = pendingRequests[envelope.inResponseTo];
if (!pr)
return; // reponse came after timeout -- too late
pr.push(envelope);
return;
}
}
for (var i = 0; i < listenersArray.length; i++) {
if (envelope.rsvp)
listenersArray[i](envelope.message, envelope, responderFor(envelope));
else
listenersArray[i](envelope.message, envelope);
}
}
return {
broadcast: broadcast,
unicast: unicast,
onReceive: onReceive,
request: request,
id: myId
};
}
})(window);