doPost.ts

global.doPost = (e: GASWebEvent): GoogleAppsScript.Content.TextOutput => {
  const command: string = e.parameter.command;
  if (command) {
    /* register commands like
        global.slackCommands.command = (params: SlackCommansParams): {} => {}; */
    const res = global.slackCommands[command.substr(1)](e.parameter); // '/command' -> 'command'
    const response = ContentService.createTextOutput();
    response.setMimeType(ContentService.MimeType.JSON);
    response.setContent(JSON.stringify(res));
    return response;
  }
};