When Should You Use Dynamic Import in React/Next.js? (With Performance Comparison)

Dynamic import lets you lazy load components so they’re only loaded when needed, instead of bundling everything up front.

1) What is Dynamic Import?

// Static import (always in initial bundle) import BigChart from "./BigChart" // Dynamic import (code-split, loaded on demand) import dynamic from "next/dynamic" const BigChart = dynamic(() => import("./BigChart")) 

2) Why Use It?

✅ Faster initial load (smaller JS)

✅ Conditional loading (only when needed)

✅ Avoid SSR issues for client-only libs ({ ssr: false })

3) Good Use Cases

• Heavy, optional widgets: charts, maps, rich editors, modals
• Client-only libs that access window
• Feature flags / A/B tests
• Dashboards with many expandable panels

4) Real-World Examples

a) Rich text editor (react-quill)

import dynamic from "next/dynamic" const RichTextEditor = dynamic(() => import("react-quill"), { ssr: false }) export default function Page() { return ( <div> <h1>Create Post</h1> <RichTextEditor theme="snow" /> </div> ) } 

b) Charts (react-chartjs-2)

import dynamic from "next/dynamic" const Chart = dynamic(() => import("react-chartjs-2"), { ssr: false }) export default function Dashboard() { return ( <section> <h2>Analytics</h2> <Chart type="bar" data={{ labels: ["A","B","C"], datasets: [{ data: [12,19,3] }] }} /> </section> ) } 

5) Performance Comparison (Before vs After)

Below is a sample comparison showing how dynamic import can change bundle breakdown.

Use the measurement steps in the next section to produce your actual numbers.

* LCP depends on network/device; treat this as illustrative. Your actual metrics may vary.

6) How to Measure It in Your App

Option A — @next/bundle-analyzer

1. Install

npm i -D @next/bundle-analyzer 

1. Configure next.config.js

// next.config.js const withBundleAnalyzer = require('@next/bundle-analyzer')({ enabled: process.env.ANALYZE === 'true', }) module.exports = withBundleAnalyzer({ // your Next.js config }) 

1. Build & Analyze

ANALYZE=true next build # Then open the generated treemaps (usually in .next/analyze) to inspect chunks. 

Option B — Inspect build output

next build # Check "First Load JS shared by all" and per-route sizes in terminal output. 

Option C — Web Vitals in production

• Track LCP/TTFB/CLS before vs after with your analytics (e.g., Vercel Web Analytics, Sentry, or custom).

7) When NOT to Use It

• Small, shared UI primitives (buttons, inputs)
• Components present on every route (header, footer)
• Over-splitting into too many tiny chunks (extra requests/latency)

8) Cheatsheet (TL;DR)

Pro tip: Pair dynamic imports with skeletons or loading placeholders so the UI feels responsive while chunks load.

Originally published on: Bitlyst