rsnext/errors/improper-devtool.md
James Mosier 435bf65784
Warn/revert custom devtool in development mode (#14285)
Warn users and revert their `devtool` when they manually change the `devtool` in development mode. For this addition, I check to ensure the `devtool` is custom (i.e. different than what is set by Next) and has a value (`false` is fine as a custom `devtool`!).

As described in [this issue (13963)](https://github.com/vercel/next.js/issues/13963), changing the `devtool` in development mode can cause issues with performance.

Fixes #13963
2020-06-24 04:15:57 +00:00

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# Improper webpack `devtool` used in development mode
#### Why This Error Occurred
Next.js chooses the most optimal `devtool` for use with webpack. Changing the `devtool` in development mode will cause severe performance regressions with your application.
#### Possible Ways to Fix It
Please remove the custom `devtool` override or only apply it to production builds in your `next.config.js`.
```js
module.exports = {
webpack: (config, options) => {
if (!options.dev) {
config.devtool = options.isServer ? false : 'your-custom-devtool'
}
return config
},
}
```