title: Confusion around typescript errors when typings seemingly exist
body: <p>I'm working on a <code>react-native</code> project that is utilising the package <code>react-native-firebase</code> as a solution to providing remote and local notifications.</p>
  
  <p>All is well, if I do the following:</p>
  
  <pre><code>import firebase from 'react-native-firebase'
  
  ...
  const messagingPermission = await firebase.messaging().hasPermission()
  </code></pre>
  
  <p>The above code runs fine and has no complaints to be made. However,</p>
  
  <pre><code>import firebase from 'react-native-firebase'
  
  ...
  const customNotification = new firebase.notifications.Notification()
  </code></pre>
  
  <p>Complains with </p>
  
  <pre><code>[ts] Property 'Notification' does not exist on type '{ (): Notifications; 
  nativeModuleExists: boolean }'
  </code></pre>
  
  <p>However if I follow through the typings (ctrl+click) then I can see the class <code>Notifications</code> there and typed up.</p>
  
  <p>Am I missing a vital Typescript lesson here or gotcha that I have overlooked? I'm positive the package is typed correctly so what is going on here?</p>
  
  <p>I can provide my <code>tsconfig.json</code> if you think it would be helpful.</p>
  
  <pre><code>{
      "compilerOptions": {
          "target": "es2015",
          "module": "es2015",
          "moduleResolution": "node",
          "allowSyntheticDefaultImports": true,
          "noImplicitAny": false,
          "preserveConstEnums": true,
          "allowJs": false,
          "sourceMap": true,
          "noImplicitReturns": true,
          "noUnusedParameters": true,
          "noUnusedLocals": true,
          "watch": false,
          "skipLibCheck": true,
          "jsx": "react",
          "outDir": "artifacts",
          "rootDir": "src",
          "baseUrl": "src",
    },
    "filesGlob": [
        "typings/index.d.ts",
        "app/**/*.ts",
        "app/**/*.tsx"
    ],
    "types": [
        "react",
        "react-native",
        "jest"
    ],
    "exclude": [
        "android",
        "ios",
        "build",
        "node_modules"
    ],
    "compileOnSave": true
  }
  </code></pre>
  
  <p>Edit: Added tsconfig</p>