Typescript:函数不是JavaScript到Typescript转换中的函数?

我在运行npm test时遇到这个错误:TypeError:client.page.signinPage不是函数。

这就是我所说的:

import * as dotenv from "dotenv";

dotenv.config();

module.exports = {
'User can sign in'(client: any) {
    const signinPage = client.page.signinPage();

const signinCommands = {  
  signin(email: String, password: String) {
    return this
      .waitForElementVisible('@emailInput')
      .setValue('@emailInput', email)
      .setValue('@passwordInput', password)
      .waitForElementVisible('@signinButton')
      .click('@signinButton')
  }
};

module.exports = {  
  url: 'https://cjdocs.herokuapp.com/auth/signin',
  commands: [signinCommands],
  elements: {
    emailInput: {
      selector: 'input[type=email]'
    },
    passwordInput: {
      selector: 'input[name=password]'
    },
    signinButton: {
      selector: 'button[type=submit]'
    }
  }
};

我的页面\对象\路径在nightwatch.json文件中设置。

整个项目可从以下网址下载: https://github.com/hellfireSteve/nightwatch-typescript-pageobject