develop

name	develop
description	Expert Azure Functions (Node.js) developer for MMO FES Function App. Use when: implementing features, fixing bugs, refactoring code, researching codebase, planning solutions. Covers timer/HTTP triggers, retry patterns, App Insights integration.
license	OGL-UK-3.0
metadata	{"author":"mmo-fes","version":"1.0"}

Function App — Developer Skill

Expert software engineer for the MMO FES Azure Function App. Reads the codebase, researches, plans, reasons, writes production-ready code following Azure Functions conventions.

When to Use

• Implementing or modifying timer/HTTP triggered functions
• Working on retry logic or error handling
• Integrating with Application Insights
• Refactoring or restructuring function code
• Any production code writing task

Workflow

Before Making Changes

1. Search codebase for similar function patterns
2. Check existing tests to understand expected behavior
3. Review function.json trigger configuration
4. Understand the retry and backoff patterns in use

During Implementation

1. Follow all mandatory rules from the auto-loaded instruction files (azure-functions.instructions.md, typescript.instructions.md)
2. Initialize App Insights BEFORE creating Axios instances — order matters
3. Export functions via module.exports = func (Node.js Azure Functions pattern)

After Implementation

1. Run tests: npm test
2. Verify coverage thresholds: 90% branches, functions, lines, statements
3. Check problems panel for any issues
4. Invoke the /unit-tests skill to write or update tests

Project Conventions

Function Handler Pattern

const func = async (context, myTimer, overrideConfig) => {
  context.log(`[COMPONENT][ACTION][STARTED]`, timeNow());
  config = { ...config, ...overrideConfig };
  if (myTimer.IsPastDue)
    context.log('[SCHEDULED-JOBS][COMPONENT][RUNNING-LATE]', timeNow());
  if (config.instrumentationKey)
    appInsights.init(config.instrumentationKey, context);
  // Business logic...
};

module.exports = func;

Retry with Exponential Backoff

async function makeApiCallWithRetry(url, apiName, key, data, maxRetries, retryDelay) {
  let retryCount = 0;
  while (retryCount < maxRetries) {
    try {
      const response = await axios.put(`${url}${apiName}`, data, {
        headers: { 'X-API-KEY': key, 'accept': 'application/json' }
      });
      return response;
    } catch (error) {
      retryCount++;
      if (retryCount >= maxRetries) throw new Error('Max retries exceeded');
      await new Promise(resolve =>
        setTimeout(resolve, Math.pow(2, retryCount) * retryDelay)
      );
    }
  }
}

Linear Retry with Delay Calculation

const retry = (fn, retries, delayFn) =>
  fn(retries).catch(e =>
    (retries > 0)
      ? wait(delayFn(retries)).then(() => retry(fn, retries - 1, delayFn))
      : Promise.reject(new Error('failed'))
  );

const calcDelay = (delay, totalRetries) => (retriesRemaining) =>
  (totalRetries - retriesRemaining) * delay;

App Insights Tracking

const trackEvent = (name, properties) => {
  if (appInsightsClient) {
    appInsightsClient.trackEvent({
      name, properties,
      tagOverrides: operationIdOverride
    });
  }
};

Bracketed Logging with Timestamps

const timeNow = () => new Date(Date.now()).toISOString();
context.log(`[SCHEDULED-JOBS][LANDING-AND-REPORTING][STARTED]`, timeNow());

Anti-Patterns

Mandatory rules in the instruction files also apply. The items below are additional anti-patterns specific to this skill:

• Initializing Axios before App Insights — App Insights must be initialized first
• Forgetting IsPastDue check on timer triggers
• Using exports.handler instead of module.exports = func
• Hardcoding retry delay without exponential backoff calculation