JAVASCRIPT

react native scaling font

<Text
    numberOfLines={1}// add this
    adjustsFontSizeToFit// add this
    style={{textAlign:'center',fontSize:30}}
  >

react native font based on viewport dimensions

<View>
  <Text
    numberOfLines={1}
    adjustsFontSizeToFit
    style={{textAlign:'center',fontSize:30}}
  >
    {this.props.email}
  </Text>
</View>