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Reference count calls to start/stopListening on ScalarMessaging (#1164)

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Otherwise component mounting/unmounting can race and you end up with nothing
listening.
This commit is contained in:
Kegsay
2017-06-30 15:42:51 +01:00
committed by GitHub
parent b8941f76d3
commit 11309f34e3
1 changed files with 17 additions and 2 deletions
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15
src/ScalarMessaging.js
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@@ -564,12 +564,27 @@ const onMessage = function(event) {
}); });
}; };
let listenerCount = 0;
module.exports = { module.exports = {
startListening: function() { startListening: function() {
if (listenerCount === 0) {
window.addEventListener("message", onMessage, false); window.addEventListener("message", onMessage, false);
}
listenerCount += 1;
}, },
stopListening: function() { stopListening: function() {
listenerCount -= 1;
if (listenerCount === 0) {
window.removeEventListener("message", onMessage); window.removeEventListener("message", onMessage);
}
if (listenerCount < 0) {
// Make an error so we get a stack trace
const e = new Error(
"ScalarMessaging: mismatched startListening / stopListening detected." +
" Negative count"
);
console.error(e);
}
}, },
}; };