Download file NodeJS with ExpressJS and AngularJS

I'm trying to make a file downloadable but it's not working, could you tell me where is my mistake ? Server-side :

app.get("/telechargement/propt", function (req, res) {
    var propt = [];
    testDb.find({}).sort({ createdAt: -1 }).exec(function (err, docs) {
        var propt = docs;
        var propt_xls = json2xls(propt);
        fs.writeFileSync('propt_conv.xlsx', propt_xls, 'binary');
        res.set('Content-Type', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
        res.download('propt_conv.xlsx');
    });
});

testDb.find is just a noSQL resquest to my NeDB database.

AngualarJS-side :

$scope.exportXLS = function() {
        $http.get("/telechargement/propt").then(function(response){
        });
    }

I guess the mistake is AngularJS-side but I don't know what to do with the response in download case.

HTML-side :

<a href="#" ng-click="exportXLS();">DL</a>

via Tewan