To understand the regular expression used in Webpack's SplitChunksPlugins CacheGroup [duplicate]

I'm trying to migrate Webpack 3 to Webpack 4 which forces us to use Split Chunks Plugin.

Split Chunks Plugin uses cacheGroups object as a way to group the chunks together. In any of those cache groups, there is a test property which says

vendors: {
  test: /[\\/]node_modules[\\/]/,
  priority: -10
}

My question is what is [\\/] in the regular expression. I know forward slashes should be escaped because they are regular expression's reserved characters but IMO, it should be

vendors: {
  test: /\/node_modules\//,
  priority: -10
}

Can anyone please explain the difference?

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