Dynamic Imports and Code Splitting in Next.js

Performance work often starts with bundle size because bundle size is easy to point at. A large JavaScript bundle clearly feels like a problem. The harder question is what to do about it without turning the application into a collection of awkward loading states and fragmented user journeys.

That is where dynamic imports and code splitting come in.

Next.js gives us a cleaner way to defer some code until it is actually needed, rather than shipping everything in the initial page load by default.

Code Splitting Means Not All Code Has to Load at Once

In a traditional bundled application, a lot of JavaScript may be included in the first load even if the user never touches the corresponding feature.

Code splitting changes that by breaking the application into smaller chunks that can be loaded later.

This matters because many features are conditional:

• a modal that opens occasionally
• an admin‑only panel
• a charting library below the fold
• a client‑only widget on one route

If a feature is not needed immediately, it can be a good candidate for delayed loading.

Next.js provides next/dynamic

The usual API looks like this:

import dynamic from 'next/dynamic';const HeavyChart = dynamic(() => import('../components/HeavyChart'));

Now the component is loaded dynamically rather than bundled in the same way as a normal static import.

This is a good example of Next.js making a performance technique feel like an ordinary component decision rather than a bundler exercise.

The Simplest Win is Deferring Expensive UI

Suppose a chart component depends on a large library and only appears after a user opens an analytics tab.

Loading it dynamically means the initial route does not have to pay that full cost up front. That can improve the experience for the majority of visitors who may never even open the chart.

That kind of selective loading is much more than a tidy demo trick. On the Nando’s UK & Ireland Replatform, not every journey needed every feature up front, so splitting code properly helped keep the experience fast without carving the UI into awkward little fragments.

This is one of the strongest arguments for code splitting: pay for features closer to when the user actually asks for them.

A Loading State Often Belongs with the Split

Dynamic imports are not just about the import statement. They also affect the interface, because a component that loads later may need a fallback.

Next.js lets us provide one:

const HeavyChart = dynamic(() => import('../components/HeavyChart'), {  loading: () => <p>Loading chart…</p>,});

That is an important part of the user experience. Performance work should not make the application feel broken while code arrives.

Not Every Component Should Be Split

This is where restraint matters.

If we split tiny, frequently used components simply because we can, the result may be:

• extra requests
• more loading states
• a more fragmented UI
• complexity without meaningful gain

Good code splitting follows actual product boundaries and actual cost, not abstract enthusiasm for smaller chunks.

ssr: false changes the behaviour further

Sometimes a component should only render on the client, perhaps because it depends heavily on browser‑only APIs.

Next.js allows that:

const BrowserOnlyWidget = dynamic(  () => import('../components/BrowserOnlyWidget'),  { ssr: false },);

This can be helpful, but it is not something to reach for casually. Disabling server rendering changes the page behaviour and can reduce how much useful markup exists up front.

So it is best used when the component genuinely cannot or should not render on the server.

Dynamic Imports are a Performance Tool, Not an Architectural Identity

Teams sometimes start treating code splitting as though more of it must always mean more sophistication.

That is not really how performance work behaves in practice.

A split is worthwhile when it removes real initial‑load cost from features users do not need immediately. It is much less convincing when it adds indirection to code that already loads at the right time.

Route‑Level Splitting and Component‑Level Splitting are Different

Next.js already gives us some code‑splitting benefits through routing, because pages naturally form chunks.

Dynamic imports become especially interesting when we need finer control within a page:

• a large optional component
• a feature hidden behind interaction
• a client‑only integration

This is where the technique earns its place.

Beware of Splitting Around Tiny Abstractions

If every modal, dropdown, and small utility widget becomes dynamically imported, the codebase may become harder to follow while the real performance gains remain modest.

That is why the strongest candidates are usually the heavier pieces:

• charts
• editors
• map libraries
• admin tools
• large third‑party integrations

Code splitting should remove real cost, not just create the appearance of optimisation.

The Product Journey Still Matters

Imagine a checkout flow split into so many small chunks that every step produces a visible loading pause. The JavaScript bundle metrics may look improved, but the user journey may feel worse.

This is why performance work is not only about bytes. It is about when the user experiences cost and whether the delay lands in a tolerable place.

A Good Rule of Thumb

Consider dynamic imports when a component is:

• large
• optional
• hidden behind user action
• not needed for the first render

Be cautious when the component is:

• tiny
• critical to the first screen
• needed almost immediately anyway

Keep the First Render Focused

Dynamic imports and code splitting in Next.js are useful because they let us align JavaScript delivery more closely with real user behaviour. Used well, they stop the first render carrying the cost of features the user has not asked for yet, whilst still letting those features load when they are genuinely needed.

When used with that discipline, next/dynamic becomes one of the more practical performance tools in the framework.