Devtool

此选项控制是否生成,以及如何生成 source map。

使用 SourceMapDevToolPlugin 进行更细粒度的配置。查看 source-map-loader 来处理已有的 source map。

devtool

string = 'eval' false

选择一种 source map 格式来增强调试过程。不同的值会明显影响到构建(build)和重新构建(rebuild)的速度。

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).

其中一些值适用于开发环境,一些适用于生产环境。对于开发环境,通常希望更快速的 source map,需要添加到 bundle 中以增加体积为代价,但是对于生产环境,则希望更精准的 source map,需要从 bundle 中分离并独立存在。

品质说明(quality)

打包后的代码 - 将所有生成的代码视为一大块代码。你看不到相互分离的模块。

生成后的代码 - 每个模块相互分离,并用模块名称进行注释。可以看到 webpack 生成的代码。示例:你会看到类似 var module__WEBPACK_IMPORTED_MODULE_1__ = __webpack_require__(42); module__WEBPACK_IMPORTED_MODULE_1__.a();,而不是 import {test} from "module"; test();

转换过的代码 - 每个模块相互分离,并用模块名称进行注释。可以看到 webpack 转换前、loader 转译后的代码。示例:你会看到类似 import {test} from "module"; var A = function(_test) { ... }(test);,而不是 import {test} from "module"; class A extends test {}

原始源代码 - 每个模块相互分离,并用模块名称进行注释。你会看到转译之前的代码,正如编写它时。这取决于 loader 支持。

无源代码内容 - source map 中不包含源代码内容。浏览器通常会尝试从 web 服务器或文件系统加载源代码。你必须确保正确设置 output.devtoolModuleFilenameTemplate,以匹配源代码的 url。

(仅限行) - source map 被简化为每行一个映射。这通常意味着每个语句只有一个映射(假设你使用这种方式)。这会妨碍你在语句级别上调试执行,也会妨碍你在每行的一些列上设置断点。与压缩后的代码组合后,映射关系是不可能实现的,因为压缩工具通常只会输出一行。

对于开发环境

以下选项非常适合开发环境:

eval - 每个模块都使用 eval() 执行,并且都有 //@ sourceURL。此选项会非常快地构建。主要缺点是,由于会映射到转换后的代码,而不是映射到原始代码(没有从 loader 中获取 source map),所以不能正确的显示行数。

eval-source-map - 每个模块使用 eval() 执行,并且 source map 转换为 DataUrl 后添加到 eval() 中。初始化 source map 时比较慢,但是会在重新构建时提供比较快的速度,并且生成实际的文件。行数能够正确映射,因为会映射到原始代码中。它会生成用于开发环境的最佳品质的 source map。

eval-cheap-source-map - 类似 eval-source-map,每个模块使用 eval() 执行。这是 "cheap(低开销)" 的 source map,因为它没有生成列映射(column mapping),只是映射行数。它会忽略源自 loader 的 source map,并且仅显示转译后的代码,就像 eval devtool。

eval-cheap-module-source-map - 类似 eval-cheap-source-map,并且,在这种情况下,源自 loader 的 source map 会得到更好的处理结果。然而,loader source map 会被简化为每行一个映射(mapping)。

特定场景

以下选项对于开发环境和生产环境并不理想。他们是一些特定场景下需要的,例如,针对一些第三方工具。

inline-source-map - source map 转换为 DataUrl 后添加到 bundle 中。

cheap-source-map - 没有列映射(column mapping)的 source map,忽略 loader source map。

inline-cheap-source-map - 类似 cheap-source-map,但是 source map 转换为 DataUrl 后添加到 bundle 中。

cheap-module-source-map - 没有列映射(column mapping)的 source map,将 loader source map 简化为每行一个映射(mapping)。

inline-cheap-module-source-map - 类似 cheap-module-source-map,但是 source mapp 转换为 DataUrl 添加到 bundle 中。

对于生产环境

这些选项通常用于生产环境中:

(none)(省略 devtool 选项) - 不生成 source map。这是一个不错的选择。

source-map - 整个 source map 作为一个单独的文件生成。它为 bundle 添加了一个引用注释,以便开发工具知道在哪里可以找到它。

hidden-source-map - 与 source-map 相同,但不会为 bundle 添加引用注释。如果你只想 source map 映射那些源自错误报告的错误堆栈跟踪信息,但不想为浏览器开发工具暴露你的 source map,这个选项会很有用。

nosources-source-map - 创建的 source map 不包含 sourcesContent(源代码内容)。它可以用来映射客户端上的堆栈跟踪,而无须暴露所有的源代码。你可以将 source map 文件部署到 web 服务器。