TypeScript support in Next.js - Performance & Optimization

Performance: TypeScript support in Next.js

MEDIUM IMPACT

This affects the build time and initial page load speed due to type checking and transpilation steps.

Adding TypeScript support in a Next.js project

NextJS

next.config.js:
module.exports = {
  typescript: {
    ignoreBuildErrors: false
  }
};

Ensures type errors are fixed before build, preventing runtime issues and improving overall app stability and user experience.

📈 Performance GainPrevents runtime errors that could block rendering or cause slow interactions, improving INP and LCP.

Adding TypeScript support in a Next.js project

NextJS

next.config.js:
module.exports = {
  typescript: {
    ignoreBuildErrors: true
  }
};

Ignoring TypeScript build errors can lead to runtime bugs and unstable builds, causing unexpected user experience issues.

📉 Performance CostMay cause runtime errors that degrade user experience and increase INP due to unexpected failures.

Performance Comparison

Pattern	Build Time	Runtime Impact	User Experience	Verdict
Ignoring type errors	Fast build but unstable	High risk of runtime errors	Poor due to crashes or bugs	[X] Bad
Strict type checking with incremental build	Moderate build time	No runtime penalty	Stable and smooth UX	[OK] Good

Rendering Pipeline

TypeScript support affects the build step before the browser rendering pipeline. It adds a transpilation and type-checking phase that delays when JavaScript is ready to be sent to the browser.

→Build Time

→JavaScript Parsing

⚠️ BottleneckBuild Time due to type-checking and transpilation

Core Web Vital Affected

LCP

This affects the build time and initial page load speed due to type checking and transpilation steps.

Optimization Tips

1Fix TypeScript errors to avoid runtime bugs and improve user experience.

2Enable incremental compilation to speed up builds and reduce delays.

3TypeScript adds build-time cost but no direct runtime penalty if configured well.

Performance Quiz - 3 Questions

How does enabling strict TypeScript checking in Next.js affect performance?

A Decreases build time and runtime errors

B Has no effect on build time or runtime

C Increases build time but prevents runtime errors

D Causes runtime errors to increase

DevTools: Performance

How to check: Record a build and page load in DevTools Performance panel. Check for long scripting or parsing times caused by large JS bundles.

What to look for: Look for long build times in terminal and large JS parsing times in DevTools indicating heavy transpiled output.