It took me a while to figure this out, so I’ll share my code here.
You will need the `file-saver` and `xlsx` npm packages.
There are two important parts:
1. Make sure you specify the `meta` section in systemjs or else it won’t load `XLSX.utils`
2. Use the correct `XLSX.write` parameters, otherwise you will get `nodebuffer is not supported by this browser`