download a file javascript dynamic file type code example
Example: how to set a var in js to be a download
var textToSave = 'this is a test';
var hiddenElement = document.createElement('a');
hiddenElement.href = 'data:attachment/text,' + encodeURI(textToSave);
hiddenElement.target = '_blank';
hiddenElement.download = 'myFile.txt';
hiddenElement.click();