What are loaders in webpack and what are they used for?

0-2 years experience

1. 1You need to add support for importing .scss files in a small React project using webpack. Walk me through how you would configure a loader to handle those files.
2. 2If you forget to install css-loader and try to import a CSS file, what error would you see during the build?
3. 3How would you limit a loader to only process files inside the src directory?

2-5 years experience

1. 1Your team added a new third‑party library that ships ES6 source files. After updating the webpack config, the bundle size grew unexpectedly. How would you investigate whether the loader configuration is causing the issue?
2. 2We have a legacy codebase that uses both Babel and TypeScript. Explain how you would set up loaders to handle .ts and .tsx files without conflicts, and what trade‑offs you consider.
3. 3During CI, a build fails with 'Module parse failed: Unexpected token' after adding a .svg import. How would you debug the loader chain to fix it?

5-8 years experience

1. 1Our application serves large images and we want to inline small icons but emit larger files. Design a loader strategy that balances bundle size and caching, and discuss any performance implications.
2. 2We need to migrate from a custom loader written in Node to a community loader, but the custom loader does special string replacement. How would you evaluate the risk and ensure parity during the migration?
3. 3Explain how you would configure webpack to use multiple loaders (e.g., babel-loader, ts-loader) in a way that minimizes build time for a monorepo with many packages.

8+ years experience

1. 1Across several teams, we have inconsistent loader configurations leading to duplicated processing and larger bundles. Propose an organization‑wide strategy for standardizing loader usage, including versioning, shared configs, and migration path.
2. 2Our product is moving from webpack to a newer bundler, but we must keep support for existing custom loaders that perform proprietary transformations. How would you approach the decision to rewrite, wrap, or deprecate these loaders while minimizing technical debt?
3. 3Discuss the long‑term maintenance implications of relying on loader plugins that are not actively maintained, and how you would set up monitoring and fallback plans.