Kevin,
I am already using my own JS code in my custom SAPUI5 Fiori app.
Please read my first question top of page:
window.open( uri , 'blank');
That is similar to "download" attr from link you send.
window.open( uri, 'blank'); is working fine in safari and chrome browser apps, but not in SAP Fiori client app.
in SAP Fiori client app the window.open( uri, 'blank'); is opened by attachment viewer ! not same as in safari / chrome app as new browser window.
in Safari / Chrome app the window.open( uri, 'blank'); is opened in new window with ability to save / download.