how to disable rotation in React Native?

React Native app is pretty much just a normal iOS application, so you can do it in exactly the same way as you do for all other apps. Simply uncheck (in XCode) the "Landscape Left" and "Landscape Right" as allowed Device Orientations in the General application properties:

For iOS, Jarek's answer is great.

For Android, you need to edit the AndroidManifest.xml file. Add the following line to each activity that you want to lock into portrait mode:

android:screenOrientation="portrait" 

So, a full example might look like this:

      <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:configChanges="keyboard|keyboardHidden|orientation|screenSize"
        android:windowSoftInputMode="adjustResize"
        android:screenOrientation="portrait">

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
      </activity>

See full list of available screenOrientation properties in the docs, here: https://developer.android.com/guide/topics/manifest/activity-element.html