JS - Add the basic architecture to be able to execute embedded js

src/scripting_api/proxy.js

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+/* Copyright 2020 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class ProxyHandler {
+  constructor(dispatchEventName) {
+    this.dispatchEventName = dispatchEventName;
+  }
+
+  get(obj, prop) {
+    if (obj._isApp && prop === this.dispatchEventName) {
+      // a backdoor to be able to call _dispatchEvent method
+      // the value of 'dispatchEvent' is generated randomly
+      // and injected in the code
+      return obj._dispatchEvent.bind(obj);
+    }
+
+    // script may add some properties to the object
+    if (prop in obj._expandos) {
+      const val = obj._expandos[prop];
+      if (typeof val === "function") {
+        return val.bind(obj);
+      }
+      return val;
+    }
+
+    if (typeof prop === "string" && !prop.startsWith("_") && prop in obj) {
+      // return only public properties
+      // i.e. the ones not starting with a '_'
+      const val = obj[prop];
+      if (typeof val === "function") {
+        return val.bind(obj);
+      }
+      return val;
+    }
+
+    return undefined;
+  }
+
+  set(obj, prop, value) {
+    if (typeof prop === "string" && !prop.startsWith("_") && prop in obj) {
+      const old = obj[prop];
+      obj[prop] = value;
+      if (obj._send && obj._id !== null && typeof old !== "function") {
+        const data = { id: obj._id };
+        data[prop] = value;
+
+        // send the updated value to the other side
+        obj._send(data);
+      }
+    } else {
+      obj._expandos[prop] = value;
+    }
+    return true;
+  }
+
+  has(obj, prop) {
+    return (
+      prop in obj._expandos ||
+      (typeof prop === "string" && !prop.startsWith("_") && prop in obj)
+    );
+  }
+
+  getPrototypeOf(obj) {
+    return null;
+  }
+
+  setPrototypeOf(obj, proto) {
+    return false;
+  }
+
+  isExtensible(obj) {
+    return true;
+  }
+
+  preventExtensions(obj) {
+    return false;
+  }
+
+  getOwnPropertyDescriptor(obj, prop) {
+    if (prop in obj._expandos) {
+      return {
+        configurable: true,
+        enumerable: true,
+        value: obj._expandos[prop],
+      };
+    }
+
+    if (typeof prop === "string" && !prop.startsWith("_") && prop in obj) {
+      return { configurable: true, enumerable: true, value: obj[prop] };
+    }
+
+    return undefined;
+  }
+
+  defineProperty(obj, key, descriptor) {
+    Object.defineProperty(obj._expandos, key, descriptor);
+    return true;
+  }
+
+  deleteProperty(obj, prop) {
+    if (prop in obj._expandos) {
+      delete obj._expandos[prop];
+    }
+  }
+
+  ownKeys(obj) {
+    const fromExpandos = Reflect.ownKeys(obj._expandos);
+    const fromObj = Reflect.ownKeys(obj).filter(k => !k.startsWith("_"));
+    return fromExpandos.concat(fromObj);
+  }
+}
+
+export { ProxyHandler };