Create A Simple Mpesa Wallet With Typescript and Express

Creating a complete M-Pesa wallet requires a more extensive implementation involving integration with payment gateways and mobile network operators, which is beyond the scope of this article. However, this post provides a basic outline to get you started with a simple M-Pesa wallet using TypeScript and Express.js.

Prerequisites:

Node.js and npm (Node Package Manager) installed on your machine.
Basic knowledge of TypeScript and Express.js.

Here's an outline of the implementation:

Set up the project: Create a new directory for your project and initialize a new Node.js project with npm.

mkdir mpesa-wallet
cd mpesa-wallet
npm init

Install required packages: Install Express.js and other necessary dependencies.

npm install express body-parser --save
npm install typescript ts-node --save-dev

Create the TypeScript configuration file (tsconfig.json):

{
  "compilerOptions": {
    "target": "ES2019",
    "module": "CommonJS",
    "outDir": "./dist",
    "rootDir": "./src",
    "strict": true
  }
}

Create the Express server (src/server.ts):

import express, { Request, Response } from 'express'
import bodyParser from 'body-parser'

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

// Define your wallet routes here

app.get('/balance', (req: Request, res: Response) => {
  // Implement code to fetch and return the wallet balance
})

app.post('/deposit', (req: Request, res: Response) => {
  // Implement code to handle wallet deposits
})

app.post('/withdraw', (req: Request, res: Response) => {
  // Implement code to handle wallet withdrawals
})

const PORT = 3000
app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`)
})

Implement the wallet logic (src/wallet.ts):

interface Wallet {
  balance: number
}

// In-memory wallet storage (for simplicity)
const wallet: Wallet = {
  balance: 0,
}

export const getBalance = (): number => {
  return wallet.balance
}

export const deposit = (amount: number): void => {
  wallet.balance += amount
}

export const withdraw = (amount: number): boolean => {
  if (wallet.balance >= amount) {
    wallet.balance -= amount
    return true
  }
  return false
}

Connect the wallet logic to the Express routes (src/server.ts):

import express, { Request, Response } from 'express'
import bodyParser from 'body-parser'
import { getBalance, deposit, withdraw } from './wallet'

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

app.get('/balance', (req: Request, res: Response) => {
  const balance = getBalance()
  res.json({ balance })
})

app.post('/deposit', (req: Request, res: Response) => {
  const { amount } = req.body
  if (!amount || typeof amount !== 'number' || amount <= 0) {
    res.status(400).json({ error: 'Invalid amount' })
  } else {
    deposit(amount)
    res.json({ message: 'Deposit successful' })
  }
})

app.post('/withdraw', (req: Request, res: Response) => {
  const { amount } = req.body
  if (!amount || typeof amount !== 'number' || amount <= 0) {
    res.status(400).json({ error: 'Invalid amount' })
  } else {
    const success = withdraw(amount)
    if (success) {
      res.json({ message: 'Withdrawal successful' })
    } else {
      res.status(400).json({ error: 'Insufficient balance' })
    }
  }
})

const PORT = 3000
app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`)
})

Compile and run the server:

npx tsc
node dist/server.js

Now you have a simple M-Pesa wallet implemented using TypeScript and Express.js. Keep in mind that this is a basic implementation without real payment gateway integrations, security measures, or proper error handling, which are essential for a production-ready application.