The Problem with Function Parameters

Oct 13, 2025 by wbrum.org 5 views

When working with modern JavaScript build tools like esbuild, understanding the intricacies of tree shaking is crucial for optimizing code size and performance. In this article, we will delve into the world of tree shaking and explore why adding a parameter to a function can cause it to abort.

What is Tree Shaking?

Tree shaking is a technique used by modern JavaScript build tools to remove unused code from a project. It works by analyzing the code and identifying which parts are not being used, and then removing those parts from the final bundle. This results in a smaller bundle size, which can improve the performance of the application.

The Problem with Function Parameters

When we add a parameter to a function, it can cause tree shaking to abort. But why? To understand this, let's take a closer look at the code.

The Original Code

Here is the original code:

// testcase.js
import { foo } from "./treeshake-test2.js";
export function test() {
  console.log(foo({
    foo: 'bar'
  }));
}

// testcase-2.js
import { parse, ExpensiveSchema } from "package-marked-side-effect-free";

function foo(data, options) {
  if (PRODUCTION) return data;
  return expensiveThing(data, ExpensiveSchema, options);
}

In this code, the foo function takes two parameters: data and options. The options parameter is not used in the function, but it is still present.

The Problem with Unused Parameters

When we run esbuild with the --minify flag, it will attempt to remove unused code from the project. However, in this case, the options parameter is not used, but it is still present in the function signature. This can cause tree shaking to abort, because the build tool is unable to determine whether the options parameter is used or not.

The Fix: Removing Unused Parameters

To fix this issue, we can simply remove the unused options parameter from the function signature:

// testcase-2.js
import { parse, ExpensiveSchema } from "package-marked-side-effect-free";

function foo(data) {
  if (PRODUCTION) return data;
  return expensiveThing(data, ExpensiveSchema, {});
}

By removing the unused options parameter, we can allow the build tool to properly tree shake the code and remove any unused parts.

Debugging Tree Shaking Issues

So, how can we debug tree shaking issues like this? Here are some tips:

Use the --debug flag: When running esbuild, use the --debug flag to enable debug mode. This will provide more detailed output and help you understand what is happening during the build process.
Use the --tree-shake flag: Use the --tree-shake flag to enable tree shaking and see which parts of the code are being removed.
Use a code editor with built-in debugging tools: Many code editors, such as Visual Studio Code, have built-in debugging tools that can help you understand what is happening during the build process.
Use a build tool with better tree shaking support: If you are experiencing issues with tree shaking, consider using a build tool that has better tree shaking support, such as Webpack.

Conclusion

In our previous article, we explored the impact of function parameters on tree shaking. We discussed how adding a parameter to a function can cause tree shaking to abort, and how to debug and fix these issues. In this article, we will answer some frequently asked questions about tree shaking and function parameters.

Q: What is tree shaking, and why is it important?

A: Tree shaking is a technique used by modern JavaScript build tools to remove unused code from a project. It works by analyzing the code and identifying which parts are not being used, and then removing those parts from the final bundle. This results in a smaller bundle size, which can improve the performance of the application.

Q: Why does adding a parameter to a function cause tree shaking to abort?

A: When we add a parameter to a function, it can cause tree shaking to abort because the build tool is unable to determine whether the parameter is used or not. If the parameter is not used, the build tool will not be able to remove the unused code, which can cause tree shaking to abort.

Q: How can I debug tree shaking issues?

A: To debug tree shaking issues, you can use the following tools and techniques:

Use the --debug flag when running esbuild to enable debug mode.
Use the --tree-shake flag to enable tree shaking and see which parts of the code are being removed.
Use a code editor with built-in debugging tools, such as Visual Studio Code.
Use a build tool with better tree shaking support, such as Webpack.

Q: How can I fix tree shaking issues caused by function parameters?

A: To fix tree shaking issues caused by function parameters, you can simply remove the unused parameter from the function signature. This will allow the build tool to properly tree shake the code and remove any unused parts.

Q: What are some best practices for using tree shaking?

A: Here are some best practices for using tree shaking:

Use a build tool that supports tree shaking, such as esbuild or Webpack.
Use the --tree-shake flag to enable tree shaking.
Use the --debug flag to enable debug mode and see which parts of the code are being removed.
Remove unused code and parameters to ensure that tree shaking is working correctly.
Use a code editor with built-in debugging tools to help you understand what is happening during the build process.

Q: Can I use tree shaking with other build tools?

A: Yes, you can use tree shaking with other build tools, such as Webpack or Rollup. However, the specific flags and techniques may vary depending on the build tool you are using.

Q: What are some common mistakes to avoid when using tree shaking?

A: Here are some common mistakes to avoid when using tree shaking:

Not using the --tree-shake flag to enable tree shaking.
Not removing unused code and parameters.
Not using a build tool that supports tree shaking.
Not using a code editor with built-in debugging tools to help you understand what is happening during the build process.

Conclusion

In conclusion, tree shaking is an important technique for optimizing code size and performance. By understanding how function parameters can cause tree shaking to abort, and by following best practices for using tree shaking, you can ensure that your code is properly optimized and that your application performs well.