title: Error when integrate SheetJS on Angular 4 + SystemJS (angular-seed)
body: <p>I'm using this seed project with Angular 4 and SystemJS (<a href="https://github.com/mgechev/angular-seed" rel="nofollow noreferrer">angular-seed</a>)</p>
  
  <p>And want to use SheetJS to export Excel file. I follow the instruction, can import xlsx fine, but when export file it constantly return error:</p>
  
  <pre><code>XLSX.utils.aoa_to_sheet is not a function
  </code></pre>
  
  <p>I have added to the project.config.ts</p>
  
  <pre><code> ...
   {
      name: 'xlsx',
      // Path to the package's bundle
      path: 'node_modules/xlsx/dist',
      packageMeta: {
        defaultExtension: 'js',
        main: 'xlsx.core.min.js'
      }
    }
  </code></pre>
  
  <p>And even modify the seed.config.ts</p>
  
  <pre><code>meta: {
      'xlsx': {
          exports: 'XLSX' // &lt;-- this is needed to tell SystemJS to expose XLSX
      }
  },
  map: {
      'fs': '',     // &lt;--|
      'crypto': '', // &lt;--| suppress native node modules
      'stream': '', // &lt;--|
  },
  </code></pre>
  
  <p>But still cannot make the SystemJS understand to import XLSX correctly.</p>
  
  <p>Anyone has faced this problem before can suggest me how to fix it. Any help is appreciated. Thank you.</p>