Calculate Loan Interest

import React,{ Component } from 'react';
import { View,Text,StyleSheet} from 'react-native';

export default class App extends Component {

  constructor() {
    super();
    this.state = {
      loanAmount:'50000',
      interestRate:'5',
      loanPeriod:'5',
      loanTenure:'4',
      totalAmount:'',
    };
    this.calculate = this.calculate.bind(this);
  }

  onChange(name,value) {
    switch (name) {
      case 'loanAmount':
        this.setState({
          loanAmount:value
        });
        break;
      case 'interestRate':
        this.setState({
          interestRate:value
        });
      case 'loanPeriod':
        this.setState({
          loanPeriod:value
        });
      case 'loanTenure':
        this.setState({
          loanTenure:value
        });
        break;
      default :
        return;
    }
  }

  calculate() {
    const {loanAmount,interestRate,loanPeriod,loanTenure} = this.state;
    const i = (parseInt(interestRate)/100).toFixed(2); // convert 5 to 0.05
    const J = i/loanTenure;
    const B = 1 - (1 / Math.pow(1+J,loanPeriod * loanTenure));
    const finalAmount = loanAmount * (J/B);
    const amountPayable =  Math.round(finalAmount * loanPeriod * loanTenure);
    const interestAmount = amountPayable - loanAmount;
    console.log('amount Payable',amountPayable);
    console.log('interest amount',interestAmount);
  }

  render() {
    const {loanAmount,interestRate,loanPeriod,loanTenure,totalAmount} = this.state;
      return (
        <View style={styles.container}>
          <Text onPress={()=>this.calculate()} style={styles.resultText}>Calculate </Text>
        </View>
      )
  }
}

const styles = StyleSheet.create({

  container:{
    flex:1,
    paddingTop:64
  },
  resultText: {
    fontWeight:'700',
    fontSize:19,
    marginTop:10,
    color:'black',
    textAlign:'center'
  },


});