源映射

【Source maps】

由于内联类型被空格替代，堆栈跟踪中的正确行号不需要源映射；而且 Node.js 不会生成它们。当启用 --experimental-transform-types 时，默认启用源映射。

【Since inline types are replaced by whitespace, source maps are unnecessary for correct line numbers in stack traces; and Node.js does not generate them. When --experimental-transform-types is enabled, source-maps are enabled by default.】