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.

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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"))

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2) Why Use It?

✅ Faster initial load (smaller JS)
✅ Conditional loading (only when needed)
✅ Avoid SSR issues for client-only libs ({ ssr: false })

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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

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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>
  )
}

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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.

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6) How to Measure It in Your App

Option A — @next/bundle-analyzer

1. Install

npm i -D @next/bundle-analyzer

2. 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
})

3. 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).

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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)

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8) Cheatsheet (TL;DR)

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