Node.js loan api code

Effective loan processing code in node.js

const express = require('express');
const { v4: uuidv4 } = require('uuid');

const app = express();
app.use(express.json());

const loans = {}; // In-memory storage

// Create a loan
app.post('/loans', (req, res) => {
  const { borrower, principal, annualInterestRate, termMonths } = req.body;

  if (!borrower || !principal || !annualInterestRate || !termMonths) {
    return res.status(400).json({ error: 'Missing required fields' });
  }

  const id = uuidv4();
  const loan = {
    id,
    borrower,
    principal,
    annualInterestRate,
    termMonths,
    createdAt: new Date()
  };

  loans[id] = loan;
  res.status(201).json(loan);
});

// Get loan details
app.get('/loans/:id', (req, res) => {
  const loan = loans[req.params.id];
  if (!loan) {
    return res.status(404).json({ error: 'Loan not found' });
  }
  res.json(loan);
});

// Calculate and return repayment schedule
app.get('/loans/:id/schedule', (req, res) => {
  const loan = loans[req.params.id];
  if (!loan) {
    return res.status(404).json({ error: 'Loan not found' });
  }

  const P = loan.principal;
  const r = loan.annualInterestRate / 100 / 12;
  const n = loan.termMonths;

  const monthlyPayment = r === 0
    ? P / n
    : P * r * Math.pow(1 + r, n) / (Math.pow(1 + r, n) - 1);

  let balance = P;
  const schedule = [];

  for (let month = 1; month <= n; month++) {
    const interest = balance * r;
    const principal = monthlyPayment - interest;
    balance -= principal;

    schedule.push({
      month,
      payment: +monthlyPayment.toFixed(2),
      principal: +principal.toFixed(2),
      interest: +interest.toFixed(2),
      balance: +Math.max(balance, 0).toFixed(2)
    });
  }

  res.json(schedule);
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Loan API running on port ${PORT}`);
});

A loan request

{
  "borrower": "Alice",
  "principal": 10000,
  "annualInterestRate": 5,
  "termMonths": 12
}