As a JavaScript bundler, Rollup.js plays a critical role in optimizing and packaging our code for production. However, as our project grows in complexity, it’s important to monitor and improve the build performance to ensure fast and efficient builds.

In this blog post, we’ll explore how to profile Rollup.js builds and identify performance bottlenecks using various tools and techniques.

1. Measuring Rollup.js Build Time

Before diving into the profiling process, let’s start by measuring the current build time for our Rollup.js project. To do this, we can use the time command in the command line:

time rollup -c

This will give us an overview of the total time taken by Rollup.js to build our project. We can use this as a baseline to measure the impact of our optimizations.

2. Using Chrome DevTools for Profiling

One powerful tool for profiling Rollup.js builds is the Chrome DevTools. We can use it to analyze the performance of our JavaScript modules and identify any performance bottlenecks.

To start profiling:

1. Open the project in Chrome and go to the Sources tab in DevTools.
2. Click on the Profiler tab.
3. Press the Record button to start profiling the Rollup.js build process.
4. Perform a build/run task in your project to capture the profiling data.
5. Stop the profiling by pressing the Stop button.

The profiling data will provide insights into the time taken by various JavaScript modules during the build process. Look for modules that consume a significant amount of time and analyze their code to understand the reasons behind the performance issues.

3. Using the Rollup.js --watch Mode

Rollup.js provides a --watch mode that allows us to monitor changes in our project files and automatically rebuild whenever a change is detected. This can be useful for identifying slow-performing files or plugins during the development process.

To use the --watch mode, run the following command:

rollup -c --watch

Observe the build time for each rebuild in the terminal. If you notice that certain modules or plugins consistently take longer to build, it may be worth investigating those portions of your codebase for potential optimizations.

4. Using Plugin Profiling

Rollup.js offers the ability to profile plugins individually, allowing us to identify any performance bottlenecks introduced by specific plugins. To enable plugin profiling, we can modify our Rollup configuration file:

import { createRollupConfig } from './rollup.config.js';
import { profilePlugin } from 'rollup-plugin-profile';

const config = createRollupConfig({
  // ...other configurations
  plugins: [
    profilePlugin(),
    // ...other plugins
  ],
});

export default config;

By adding the rollup-plugin-profile plugin to our configuration, we can gather detailed information about the time spent in each plugin during the build process. This data can help us identify plugins that may need optimization or replacement.

Conclusion

By profiling our Rollup.js builds, we can identify performance bottlenecks and take steps to optimize our project’s build process. From using Chrome DevTools to analyzing individual plugins, there are several techniques available to gain insights into the build performance.

Remember to periodically measure the build time and evaluate the impact of optimizations. Ultimately, this will contribute to faster builds and a more efficient development workflow.

#rollupjs #buildperformance