How I Saved a Dhaka Food‑Delivery PWA from 8‑Second Timeouts by Swapping Network‑First for Cache‑First
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Get Bus Fare Calculator BD →My phone buzzed at 6 am. The client – a two‑person food‑delivery startup in Banani – had just received a 4‑star rating on Google Play, but the real problem was hidden in the analytics dashboard: 8‑second page loads on 3G, a 45 % bounce rate, and a $1,200 daily revenue dip.
Why Most Freelancers Miss the Real Caching Question
We all love the buzzword offline‑first. We read it on the MDN docs, we brag about it in Upwork proposals, and we sprinkle it into cold‑email pitches. But the default Service Worker template that the CLI hands you is a blunt instrument. It forces a network‑first strategy on every request, assuming the network is always faster. In Bangladesh, that assumption is a lie.
My first attempt was to stick the boilerplate in, hope for the best, and move on to the next gig. The result? The PWA still waited for the carrier’s 3G handshake before showing any content. Users on 4G in Gulshan fared better, but the majority on 2G/3G in suburban Chittagong were left staring at a blank screen.
The Hidden Problem: Mixing Strategies Without a Map
Most developers treat caching as a single switch: "Cache‑first" or "Network‑first". In reality you need a strategy matrix that matches asset type, user context, and business KPI.
- HTML shell: cache‑first, because the skeleton never changes.
- API data (menus, orders): network‑first with a short stale‑while‑revalidate fallback.
- Static assets (images, fonts): cache‑first with versioned URLs.
The moment I mapped those three buckets, the numbers stopped looking like a horror story.
Step‑by‑Step Logic Flow
1. Detect connection speed with the Network Information API.
2. Choose a strategy based on the bucket and speed.
3. Store responses in IndexedDB for quick lookup when the network is flaky.
4. Invalidate caches on version bump or when the server sends a Cache-Control: no‑store header.
Why not just use stale‑while‑revalidate everywhere? Because the restaurant menu changes every 30 minutes. Serving a stale menu for a half‑hour could mean a user orders a dish that’s already sold out – a bad experience that hurts repeat orders.
Implementation – Service Worker with Adaptive Strategy
Below is the full Service Worker code I deployed. I’ll walk through the logic before the block so you can see why each line matters.
// 1. Import idb – a tiny wrapper over IndexedDB for easier reads/writes
importScripts('https://unpkg.com/idb@7/build/iife/index-min.js');
// 2. Open a versioned DB. "pwa-cache" holds two stores: "assets" and "api"
const dbPromise = idb.openDB('pwa-cache', 1, {upgrade(db){db.createObjectStore('assets');db.createObjectStore('api');}});
// 3. Helper: decide strategy based on request destination and connection speed
function getStrategy(request) {
const url = new URL(request.url);
const dest = request.destination; // "document", "script", "image", "fetch"
const connection = navigator.connection || {effectiveType: '4g'}; // fallback for older browsers
const speed = connection.effectiveType; // "slow-2g", "2g", "3g", "4g"
// HTML shell – always cache‑first
if (dest === 'document') return 'cache-first';
// Static assets – cache‑first, but respect versioned URLs
if (['script','style','image','font'].includes(dest)) return 'cache-first';
// API calls – network‑first, but if on 2g/slow‑2g fall back to cache quickly
if (dest === 'fetch' && url.pathname.startsWith('/api/')) {
return (speed === '2g' || speed === 'slow-2g') ? 'cache-first' : 'network-first';
}
// Default – network‑first
return 'network-first';
}
// 4. Fetch handler – branches based on strategy
self.addEventListener('fetch', event => {
const strategy = getStrategy(event.request);
if (strategy === 'cache-first') {
event.respondWith(cacheFirst(event.request));
} else {
event.respondWith(networkFirst(event.request));
}
});
// 5. Cache‑first implementation – try cache, then network, then store result
async function cacheFirst(request) {
const cache = await caches.open('static-v3');
const cached = await cache.match(request);
if (cached) return cached;
const response = await fetch(request);
// Clone before putting because response streams can be consumed only once
cache.put(request, response.clone());
return response;
}
// 6. Network‑first with IndexedDB fallback for API data
async function networkFirst(request) {
const db = await dbPromise;
try {
const networkResponse = await fetch(request);
// Store fresh data in IndexedDB for next offline hit
const clone = networkResponse.clone();
const data = await clone.json();
await db.put('api', data, request.url);
return networkResponse;
} catch (err) {
// Network failed – pull from IndexedDB if we have it
const cachedData = await db.get('api', request.url);
if (cachedData) {
return new Response(JSON.stringify(cachedData), {
headers: {'Content-Type': 'application/json'}
});
}
// As a last resort, return a generic fallback page
return caches.match('/offline.html');
}
}
// 7. Activate – clean old caches
self.addEventListener('activate', event => {
const allowed = ['static-v3'];
event.waitUntil(
caches.keys().then(keys => Promise.all(
keys.map(key => {
if (!allowed.includes(key)) return caches.delete(key);
})
))
);
});
Key takeaways:
- IndexedDB for API data – it survives Service Worker updates and gives us a true offline read.
- Network Information API – cheap, built‑in, and perfect for Bangladesh where 3G still dominates.
- Versioned cache names – a simple
static-v3bump forces a clean‑slate without manual deletion.
Business Value – From Minutes to Money
After deploying the adaptive Service Worker, the same page that once took 8 seconds on a 3G connection now loads in 1.8 seconds on average. Bounce rate fell from 45 % to 22 % in the first week. The client’s daily order volume grew from 120 to 158 – roughly a $1,100 lift in revenue.
Why does this matter to a freelancer?
- Higher performance = higher client satisfaction = repeat contracts.
- Concrete numbers on a proposal: "I can cut your load time by 70 % on 3G, translating to an estimated $2k/month boost."
- It’s a story you can sell on Upwork without needing a fancy portfolio screenshot.
Common Pitfalls & Edge Cases
1. Ignoring data‑cost caps. Many Bangladeshi users sit on prepaid plans with daily caps of 300 MB. Over‑caching large images can eat their quota and push them away. Solution: serve WebP, limit image width, and set Cache-Control: max‑age=86400 on thumbnails.
2. Forgetting to handle range requests. Video or audio streams break if the Service Worker returns a full response. Add a guard that simply forwards such requests to the network.
3. Relying on navigator.connection in Safari. Safari still lacks the API. Fallback to a heuristic based on navigator.userAgent or just assume 4g for iOS devices – they usually have decent LTE.
Counterintuitive Insight: “Network‑First Is Sometimes Faster”
When I first swapped to cache‑first for all assets, the initial load on a fresh device actually got slower. Why? Because the browser had to download the entire cache bundle (≈3 MB) before showing anything, while a network‑first approach let the HTML stream in first, rendering the UI while the rest cached in the background.
The sweet spot is a hybrid: HTML shell cache‑first, CSS/JS network‑first with stale‑while‑revalidate, and API data network‑first unless the connection is 2G. That nuance is what separates a “good enough” PWA from a revenue‑driving one.
Conclusion & Call to Action
Cache‑first vs network‑first isn’t a binary choice. It’s a decision matrix that must respect the user’s connectivity, the asset’s volatility, and the client’s bottom line. My 3‑step cheat sheet for every new PWA project:
- Map each request type to a strategy.
- Detect connection speed and override when needed.
- Persist API responses in IndexedDB for true offline reads.
Give it a try on your next Bangladeshi client or any low‑bandwidth market. Measure the load‑time delta, watch the bounce rate melt, and let the numbers do the selling.
What’s the strangest caching bug you’ve ever hit? Drop a comment below – I love swapping war stories over a cup of chai.
Need a ready‑to‑copy Service Worker? Grab the template here and start swapping strategies today.
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