Next js Build Time Analyzer: How to Analyze and Improve Build Times

Analyzing Next.js build times is crucial for optimizing development workflows.

A slow build time can significantly hinder your productivity and impact your team's efficiency.

The Next.js Build Time Analyzer provides valuable insights into your build process, helping you identify bottlenecks and areas for improvement.

By using the Analyzer, you can gain a deeper understanding of your build times and make data-driven decisions to optimize your workflow.

The Analyzer breaks down your build time into various components, including page rendering, code splitting, and asset optimization.

Bundle analysis is an approach for analyzing your application to identify opportunities for reducing its size. With a tool like next/bundle-analyzer, you can see what modules in your application bundle take up much space, identify unnecessary files, and find ways to reduce the size of such files or delete unused ones.

Some tools for analyzing the size of your Next.js application include next/bundle-analyzer, webpack-bundle-analyzer, and next-bundle-analyzer.

Using bundle analysis, you can optimize your codebase by identifying and removing unnecessary dependencies. For example, a Next.js web app had a form page that increased from 844B to 8.416kB when using the react-hook-form package, which was overkill for a simple form.

The unnecessary-imports branch of the example app showed that importing CSS files into the accordion page increased its size from 1.39kB to 5.26kB. This highlights the importance of understanding when to use a package or dependency.

To demonstrate the impact of optimization approaches, a simple Next.js web app was created with four pages: home, form, accordion, and carousel. The main branch of the app was fully optimized, and then other branches were built to compare their performance.

Here's a comparison of the page sizes for the main branch:

By applying optimization approaches to a more complex codebase, the build performance would be even more significant.

Next.js provides several inbuilt optimizations that can improve build performance, such as automatic static optimization, code splitting, image optimization, font optimization, and prefetching, as well as optimizing third-party scripts.

These optimizations can make a significant impact, as demonstrated by a simple Next.js web app that was created to compare the build performance of different approaches. The app has four pages: home, form, accordion, and carousel.

The project only needs one icon, and using an SVG is better than importing a package like react-icons. This can save a significant amount of space in the build.

Building a customized accordion is easy and smaller in size compared to using a package like react-accessible-accordion. This can also help reduce the build size.

For a simple form, packages like react-hook-form are overkill and can increase the build size significantly. In this example, the form page increased from 844B to 8.416kB.

The unnecessary-imports branch shows that importing unnecessary CSS files can also increase the build size. In this case, the accordion page size increased from 1.39kB to 5.26kB.

Here's a comparison of the build sizes for each page in the example app:

Understanding when to use a package or dependency can be vital in building performance. By applying these optimization approaches to a more complex codebase, the build performance would be even more significant.

Bundle analysis is an approach for analyzing your application to identify opportunities for reducing its size. You can use tools like next/bundle-analyzer, webpack-bundle-analyzer, and next-bundle-analyzer to see what modules in your application bundle take up much space and find ways to reduce the size of such files or delete unused ones.

Analyze the bundle with tools like bundle-analyzer and source-map-explorer to get a clear view of what's happening in the bundle and what could be changed.

Some libraries can be extensive and take up a lot of space, like react-syntax-highlight, which had a lot of files that were taking up a lot of space.

Here are some actions you can take to reduce the size of your bundle:

By using these tools and taking these actions, you can significantly reduce the size of your bundle. For example, the author of the article was able to shave off 30% of the bundle size by making smarter choices when it comes to library selection and feature implementation.

Using Next.js' built-in tools can greatly improve build performance. Running @next/bundle-analyzer helped reduce build times by fixing unnecessary imports.

The first step to optimizing build times is to identify the cause of lengthy compile times. To do this, you can analyze your build size by looking at the Network tab in devtools. The three largest JS files in the example are index.js at 5.6 MB, _app.js at 3.5MB, and main.js at 984K.

Fixing unnecessary imports can reduce bundle size and remove redundancy. For example, loading all of react-heroicons is unnecessary and can be fixed with more specific imports.

Using the latest stable version of Next.js can make a big difference in build performance. The team behind Next.js is constantly working to improve the framework and add new features.

As of this writing, the latest stable version is v13.4, and you can check the latest version here. You can upgrade your app to the latest stable version by running a specific command.

Updates are a crucial part of keeping our codebases efficient and up-to-date. Using tools like @next/bundle-analyzer can help identify areas for improvement.

Running @next/bundle-analyzer helped one developer optimize their build times and reduce redundancy in their code. The tool revealed that they were loading a large index.js file, which was easily fixed with more specific imports.

Analyzing bundle size is key to understanding where dependencies are used. Next.js has tools to help with this, but @next/bundle-analyzer is a popular choice for developers. By using this tool, you can see exactly which files are taking up the most space in your bundles.

Here are the three largest JS files in one developer's bundle, according to the Network tab in devtools:

Fixing those imports should reduce the bundle size and remove redundancy, as recommended by @juliomalves. This is a simple yet effective way to optimize your code and improve performance.