- Category: NextJS
Solving Next.js Build Errors with Custom Babel Configurations
Solving Next.js Build Errors with Custom Babel Configurations
Introduction:
Next.js simplifies the development process with its built-in configurations, but when you need custom libraries or advanced features like decorators, you may encounter frustrating build errors. Misconfigured Babel settings are often the root cause of these issues.
In this blog, we’ll explore common build errors related to Babel in Next.js, understand their causes, and provide solutions to configure Babel effectively for seamless builds.
Uncaught TypeError: Cannot Read Property ‘X’ of Undefined
The Problem:
Suppose you’re working on a Next.js project and want to use decorators in your codebase. After adding decorators to your files, your build suddenly fails with an error like this:
SyntaxError: Unexpected token ‘@’
Or perhaps you’ve installed a custom library that doesn’t transpile properly, resulting in an error such as:
Module parse failed: Unexpected token
@decorator
class Example {
method() {
console.log(“This is an example.”);
}
}
export default Example;
Issues
- Decorator Syntax Not Supported: The default Babel configuration in Next.js doesn’t support experimental features like decorators.
- Library Compatibility: Some custom libraries require additional Babel plugins to transpile properly.
Understanding the Issue
Next.js uses a default Babel configuration optimized for most use cases, but it doesn’t automatically include plugins for experimental or library-specific features. Without the proper Babel settings, the build process fails to parse such syntax.
The Solution:
To resolve this, you need to customize the Babel configuration by creating a babel.config.js file in your Next.js project.
how you can configure Babel to support decorators:
Install the necessary dependencies:
npm install @babel/plugin-proposal-decorators @babel/plugin-proposal-class-properties
Create or update babel.config.js in the root directory:
module.exports = {
presets: [“next/babel”], // Use Next.js default preset
plugins: [
[“@babel/plugin-proposal-decorators”, { legacy: true }],
[“@babel/plugin-proposal-class-properties”, { loose: true }]
],
};
Use the decorators without build errors:
@decorator
class Example {
method() {
console.log(“This is now supported.”);
}
}
export default Example;
Explanation
- Presets: The
next/babelpreset ensures compatibility with Next.js. - Plugins:
@babel/plugin-proposal-decoratorsadds support for decorators, and@babel/plugin-proposal-class-propertiesensures class property support.