Hi Weibotaoa have you tried looking into SKPM and SKPM-with-webview? https://github.com/skpm/sketch-module-web-view/blob/master/docs/communication-plugin-webview.md
I'm going to ignore the block for now but feel free to search around the forum here for more details on that. But to properly call the function you can send in a string and
nil for the completionHandler.