Building a Subscription Management Mini Program with Tencent Cloud Serverless Functions

With many online services offering subscription plans, managing recurring expenses becomes a common problem. The "Moly Subscription Assistant" mini‑program was created to help users conveniently track monthly subscriptions, leveraging WeChat Mini‑Program cloud development to avoid building a traditional backend server. The entire product was prototyped and launched in just five days.

The core product logic consists of three simple features: (1) users add a subscription, (2) the home page displays all subscriptions, and (3) a backend cloud function automatically calculates the average monthly expense.

Cloud development (Tencent Cloud Serverless) provides complete cloud support—cloud functions, a NoSQL database, and file storage—so developers can focus on business logic without managing servers or operations. A single qualified front‑end developer can implement the whole mini‑program.

To enable cloud development, add the field "cloudfunctionRoot":"cloudfunctions/" to project.config.json and set "cloud":true in app.json (or game.json ) for compatibility.

User authentication is handled by a cloud function that retrieves the trusted OpenID from the request context, eliminating the need for explicit user login. Example initialization in App.js :

App({
  onLaunch() {
    wx.cloud.init({ traceUser: true })
  }
})

Adding a subscription is implemented in a Node.js cloud function addUserSubscription (file main.js ):

const cloud = require('wx-server-sdk')
cloud.init()
const db = cloud.database()
exports.main = async (event, context) => {
  const wxContext = cloud.getWXContext()
  const openid = wxContext.OPENID
  const { data } = event
  return db.collection('subscriptions').add({
    data: Object.assign(data, { _openid: openid })
  })
}

Querying subscriptions uses another cloud function getUserSubscriptions :

const cloud = require('wx-server-sdk')
cloud.init()
const db = cloud.database()
exports.main = async (event, context) => {
  const wxContext = cloud.getWXContext()
  const openid = wxContext.OPENID
  return db.collection('subscriptions').where({ _openid: openid }).get()
}

After writing the functions, they can be deployed with a single "Upload and Deploy" click in the development tool, providing a fast and elegant backend deployment workflow.

On the client side, the mini‑program calls the cloud functions to retrieve the current user's subscriptions:

Page({
  data: { subscriptions: [] },
  onLoad() {
    wx.cloud.callFunction({ name: 'getUserSubscriptions' })
      .then(res => this.setData({ subscriptions: res.result.data }))
      .catch(console.log)
  }
})

To support multiple currencies, the app stores exchange rates in the cloud database and updates them periodically using a timed cloud‑function trigger. The trigger configuration ( config.json ) looks like:

{
  "triggers": [{
    "name": "updateCurrencyDaily",
    "type": "timer",
    "config": "0 0 */2 * * * *" // every 2 hours
  }]
}

The update function fetches real‑time rates from Alpha Vantage, iterates over a list of supported currencies, and writes the results back to the currency collection:

const cloud = require('wx-server-sdk')
const fetch = require('node-fetch')
cloud.init()
const db = cloud.database()
const API_KEY = 'SECRET'
const BASE_URL = `https://www.alphavantage.co/query?function=CURRENCY_EXCHANGE_RATE&to_currency=CNY&apikey=${API_KEY}`
exports.main = async (event, context) => {
  const supportCurrencyList = ['USD','JPY','EUR','GBP','HKD','AUD']
  const toCNY = {}
  for (const currency of supportCurrencyList) {
    const rate = await fetch(`${BASE_URL}&from_currency=${currency}`)
      .then(res => res.json())
      .then(res => res['Realtime Currency Exchange Rate']['5. Exchange Rate'])
    toCNY[currency] = parseFloat(rate)
  }
  return db.collection('currency').doc('some_id')
    .update({ data: Object.assign(toCNY, { date: new Date() }) })
}

Because the function uses node-fetch , the dependency must be added to package.json (e.g., "node-fetch":"^2.3.0" ) and installed via the cloud console or npm i node-fetch .

In summary, the article demonstrates how to use Tencent Cloud's serverless cloud development to quickly build a fully functional subscription‑management mini‑program, covering backend authentication, CRUD operations, scheduled tasks, and multi‑currency handling—all without provisioning any traditional servers.