implement mutualExclude factory

src/Util/mutualExclude.js

@@ -0,0 +1,15 @@
+
+export function createMutualExclude () {
+  var token = true
+  return function mutualExclude (f) {
+    if (token) {
+      token = false
+      try {
+        f()
+      } catch (e) {
+        console.error(e)
+      }
+      token = true
+    }
+  }
+}