title: How use webpack plugin to only one entry
body: <p>I want to use in webpack multiple entries using the same file, but passing a variable.</p>
  
  <p>My idea is use the webpack.definePlugin to each entry.</p>
  
  <p>Example:</p>
  
  <pre><code>{
    entry: {
      file1: 'myfile.js',
      file2: 'myfile.js',
    },
    output: {
      filename: '[name]/myjs.js'
    }
  }
  </code></pre>
  
  <p>And I set the plugins:</p>
  
  <pre><code>{
     plugins: [
       new webpack.DefinePlugin({
          MYVARTOFILE: 'a',
          filename: 'file1/myjs.js' // I want to make something like this
       }),
       new webpack.DefinePlugin({
          MYVARTOFILE: 'b',
          filename: 'file2/myjs.js' // I want to make something like this
       })
     ]
  }
  </code></pre>
  
  <p>Or if is possible passing a variable to each entry in a different way.<br>
  If is possible to:</p>
  
  <pre><code>  entry: {
      file1: 'myfile.js?variable=a',
      file2: 'myfile.js?variable=b',
    }
  </code></pre>
  
  <p>And get in my file this variable,.</p>