Devtool
This option controls if and how source maps are generated.
Use the SourceMapDevToolPlugin for a more fine grained configuration. See the source-map-loader to deal with existing source maps.
devtool
string = 'eval' false
Choose a style of source mapping to enhance the debugging process. These values can affect build and rebuild speed dramatically.
| devtool | performance | production | quality | comment |
|---|---|---|---|---|
| (none) | build: fastest rebuild: fastest | yes | bundle | Recommended choice for production builds with maximum performance. |
eval | build: fast rebuild: fastest | no | generated | Recommended choice for development builds with maximum performance. |
eval-cheap-source-map | build: ok rebuild: fast | no | transformed | Tradeoff choice for development builds. |
eval-cheap-module-source-map | build: slow rebuild: fast | no | original lines | Tradeoff choice for development builds. |
eval-source-map | build: slowest rebuild: ok | no | original | Recommended choice for development builds with high quality SourceMaps. |
cheap-source-map | build: ok rebuild: slow | no | transformed | |
cheap-module-source-map | build: slow rebuild: slow | no | original lines | |
source-map | build: slowest rebuild: slowest | yes | original | Recommended choice for production builds with high quality SourceMaps. |
inline-cheap-source-map | build: ok rebuild: slow | no | transformed | |
inline-cheap-module-source-map | build: slow rebuild: slow | no | original lines | |
inline-source-map | build: slowest rebuild: slowest | no | original | Possible choice when publishing a single file |
eval-nosources-cheap-source-map | build: ok rebuild: fast | no | transformed | source code not included |
eval-nosources-cheap-module-source-map | build: slow rebuild: fast | no | original lines | source code not included |
eval-nosources-source-map | build: slowest rebuild: ok | no | original | source code not included |
inline-nosources-cheap-source-map | build: ok rebuild: slow | no | transformed | source code not included |
inline-nosources-cheap-module-source-map | build: slow rebuild: slow | no | original lines | source code not included |
inline-nosources-source-map | build: slowest rebuild: slowest | no | original | source code not included |
nosources-cheap-source-map | build: ok rebuild: slow | no | transformed | source code not included |
nosources-cheap-module-source-map | build: slow rebuild: slow | no | original lines | source code not included |
nosources-source-map | build: slowest rebuild: slowest | yes | original | source code not included |
hidden-nosources-cheap-source-map | build: ok rebuild: slow | no | transformed | no reference, source code not included |
hidden-nosources-cheap-module-source-map | build: slow rebuild: slow | no | original lines | no reference, source code not included |
hidden-nosources-source-map | build: slowest rebuild: slowest | yes | original | no reference, source code not included |
hidden-cheap-source-map | build: ok rebuild: slow | no | transformed | no reference |
hidden-cheap-module-source-map | build: slow rebuild: slow | no | original lines | no reference |
hidden-source-map | build: slowest rebuild: slowest | yes | original | no reference. Possible choice when using SourceMap only for error reporting purposes. |
| shortcut | explanation |
|---|---|
| performance: build | How is the performance of the initial build affected by the devtool setting? |
| performance: rebuild | How is the performance of the incremental build affected by the devtool setting? Slow devtools might reduce development feedback loop in watch mode. The scale is different compared to the build performance, as one would expect rebuilds to be faster than builds. |
| production | Does it make sense to use this devtool for production builds? It's usually no when the devtool has a negative effect on user experience. |
| quality: bundled | You will see all generated code of a chunk in a single blob of code. This is the raw output file without any devtooling support |
| quality: generated | You will see the generated code, but each module is shown as separate code file in browser devtools. |
| quality: transformed | You will see generated code after the preprocessing by loaders but before additional webpack transformations. Only source lines will be mapped and column information will be discarded resp. not generated. This prevents setting breakpoints in the middle of lines which doesn't work together with minimizer. |
| quality: original lines | You will see the original code that you wrote, assuming all loaders support SourceMapping. Only source lines will be mapped and column information will be discarded resp. not generated. This prevents setting breakpoints in the middle of lines which doesn't work together with minimizer. |
| quality: original | You will see the original code that you wrote, assuming all loaders support SourceMapping. |
eval-* addition | generate SourceMap per module and attach it via eval. Recommended for development, because of improved rebuild performance. Note that there is a windows defender issue, which causes huge slowdown due to virus scanning. |
inline-* addition | inline the SourceMap to the original file instead of creating a separate file. |
hidden-* addition | no reference to the SourceMap added. When SourceMap is not deployed, but should still be generated, e. g. for error reporting purposes. |
nosources-* addition | source code is not included in SourceMap. This can be useful when the original files should be referenced (further config options needed). |
Some of these values are suited for development and some for production. For development you typically want fast Source Maps at the cost of bundle size, but for production you want separate Source Maps that are accurate and support minimizing.
Qualities
bundled code - You see all generated code as a big blob of code. You don't see modules separated from each other.
generated code - You see each module separated from each other, annotated with module names. You see the code generated by webpack. Example: Instead of import {test} from "module"; test(); you see something like var module__WEBPACK_IMPORTED_MODULE_1__ = __webpack_require__(42); module__WEBPACK_IMPORTED_MODULE_1__.a();.
transformed code - You see each module separated from each other, annotated with module names. You see the code before webpack transforms it, but after Loaders transpile it. Example: Instead of import {test} from "module"; class A extends test {} you see something like import {test} from "module"; var A = function(_test) { ... }(test);
original source - You see each module separated from each other, annotated with module names. You see the code before transpilation, as you authored it. This depends on Loader support.
without source content - Contents for the sources are not included in the Source Maps. Browsers usually try to load the source from the webserver or filesystem. You have to make sure to set output.devtoolModuleFilenameTemplate correctly to match source urls.
(lines only) - Source Maps are simplified to a single mapping per line. This usually means a single mapping per statement (assuming you author it this way). This prevents you from debugging execution on statement level and from settings breakpoints on columns of a line. Combining with minimizing is not possible as minimizers usually only emit a single line.
Development
The following options are ideal for development:
eval - Each module is executed with eval() and //@ sourceURL. This is pretty fast. The main disadvantage is that it doesn't display line numbers correctly since it gets mapped to transpiled code instead of the original code (No Source Maps from Loaders).
eval-source-map - Each module is executed with eval() and a SourceMap is added as a DataUrl to the eval(). Initially it is slow, but it provides fast rebuild speed and yields real files. Line numbers are correctly mapped since it gets mapped to the original code. It yields the best quality SourceMaps for development.
eval-cheap-source-map - Similar to eval-source-map, each module is executed with eval(). It is "cheap" because it doesn't have column mappings, it only maps line numbers. It ignores SourceMaps from Loaders and only display transpiled code similar to the eval devtool.
eval-cheap-module-source-map - Similar to eval-cheap-source-map, however, in this case Source Maps from Loaders are processed for better results. However Loader Source Maps are simplified to a single mapping per line.
Special cases
The following options are not ideal for development nor production. They are needed for some special cases, i. e. for some 3rd party tools.
inline-source-map - A SourceMap is added as a DataUrl to the bundle.
cheap-source-map - A SourceMap without column-mappings ignoring loader Source Maps.
inline-cheap-source-map - Similar to cheap-source-map but SourceMap is added as a DataUrl to the bundle.
cheap-module-source-map - A SourceMap without column-mappings that simplifies loader Source Maps to a single mapping per line.
inline-cheap-module-source-map - Similar to cheap-module-source-map but SourceMap is added as a DataUrl to the bundle.
Production
These options are typically used in production:
(none) (Omit the devtool option) - No SourceMap is emitted. This is a good option to start with.
source-map - A full SourceMap is emitted as a separate file. It adds a reference comment to the bundle so development tools know where to find it.
hidden-source-map - Same as source-map, but doesn't add a reference comment to the bundle. Useful if you only want SourceMaps to map error stack traces from error reports, but don't want to expose your SourceMap for the browser development tools.
nosources-source-map - A SourceMap is created without the sourcesContent in it. It can be used to map stack traces on the client without exposing all of the source code. You can deploy the Source Map file to the webserver.
Further Reading
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