Fixed possible surprises in background script message handling.

1 files changed, 31 insertions, 0 deletions

diff --git a/src/lib/Messages.js b/src/lib/Messages.js
new file mode 100644
index 0000000..c87a8a8
--- /dev/null
+++ b/src/lib/Messages.js
@@ -0,0 +1,31 @@
+"use strict";
+{
+  let handlers = new Set();
+  
+  let dispatch = async (msg, sender) => {
+    let {action} = msg;
+    for (let h of handlers) {
+      let f = h[action];
+      if (typeof f === "function") {
+        return await f(msg, sender);
+      }
+    }
+  };
+  
+  var Messages = {
+    addHandler(handler) {
+      let originalSize = handlers.size;
+      handlers.add(handler);
+      if (originalSize === 0 && handlers.size === 1) {
+        browser.runtime.onMessage.addListener(dispatch);
+      }
+    },
+    removeHandler(handler) {
+      let originalSize = handlers.size;
+      handlers.delete(handler);
+      if (originalSize === 1 && handlers.size === 0) {
+        browser.runtime.onMessage.remveListener(dispatch);
+      }
+    }
+  }
+}