onMessage={ev =>
            this.receiveMessage(ev, (name, data) => {
              this.log(name, data);
              if (name.startsWith("app#")) {
                const fnName = name.split("app#")[1];
                const safeFunctions = {
                  log: this.log,
                  pickImage: this.pickImage,
                  onContentsChange: this.onContentsChange
                };

                if (!safeFunctions[fnName]) {
                  throw new Error(`Function '${fnName}' does not exist`);
                }

                this.log(fnName, ...data);
                safeFunctions[fnName](...data);
              }
            })
          }