Use cheap-module-eval-source-map

[noisysocks]

By sacrificing a small amount of source map accuracy, we make incremental development builds about 20% faster.

Learn about the different modes here: https://webpack.js.org/configuration/devtool/#devtool

About the trade-off

Say you have code like this:

const { foo, bar, baz } = coolObject;

With source-maps, DevTools will allow you to step through each operation within that line: first, the foo assignment, then the bar assignment, then the baz assignment.

With cheap-module-eval-source-map, DevTools will only allow you to break at that entire line.

In my experience, it’s not worth the performance penalty.

And besides, if one needs to step through things more granularly, they can temporarily change their Webpack settings and rebuild.

[noisysocks]

I personally think the trade-off here is worth it, but happy to hear what @WordPress/gutenberg-core thinks 🙂

[gziolo]

With source-maps, DevTools will allow you to step through each operation within that line: first, the foo assignment, then the bar assignment, then the baz assignment.

With cheap-module-eval-source-map, DevTools will only allow you to break at that entire line.

Should we document it somewhere in our docs?

[gziolo]

I double checked how Calypso handles it:

devtool: isDevelopment ? '#eval' : process.env.SOURCEMAP || false, // in production builds you can specify a source-map via env var.

process.env.SOURCEMAP is also passed as param to uglify plugin:

sourceMap: Boolean( process.env.SOURCEMAP ),

[aduth]

Using breakpoints in Chrome DevTools quite frequently, I find that beyond what tends to be advertised in the source map option descriptions, Chrome is very particular about working well with some options over the other; often not creating or firing breakpoints, or not creating them where I'd expect. This is why I might be reluctant to make any changes here, though if it doesn't regress I'd be fine with the change.

To the actual difference: One more common case might be setting breakpoints at inline anonymous function callbacks, if that would be affected.