webpack entry filename config used [ext] placeholders not take effect

I’m sorry for my English is low,hope you understand.
I learning how to use webpack build my project.The following is config for two entry files:

 entry:{
    main: {
      import: "./src/main.js",
      filename:"main/[name].[hash:6][ext]",
      dependOn:"lodash"
    },
    index:{
      import:"./src/index.js",
      filename:"index/[name].[hash:6][ext]",
      dependOn:"lodash"
    },
    lodash: {import: [ "lodash" ],filename:"lodash/[name].[hash:6].js" }
  },

I think it will generator two files after I execute the npm run build script,for example,main.a24fc1.js and index.b42afd.js ,their name should look like that.

But in result they is this:

|- build
  |- index
    |- index.81c047[ext]
  |- main
    |- main.81c047[ext]

In their filename config,used [ext] placeholders but it’s not take effect.I don’t know why it happended,becouse my config the same as in webpack document’s demo.

// This is webpack demo config:
module.exports = {
  //...
  entry: {
    app: './app.js',
    home: { import: './contact.js', filename: 'pages/[name][ext]' },
    about: { import: './about.js', filename: 'pages/[name][ext]' },
  },
};

I are unable solve the problem…Thank to everyone helped me!(Please tell me if there are has any English mistakes in this article.^_^)