trigger-client-side-file-saving.js

// For more information see: https://stackoverflow.com/questions/2897619/using-html5-javascript-to-generate-and-save-a-file
var pom = document.createElement('a');
pom.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent('hello world!'));
pom.setAttribute('download', 'test.txt');

if (document.createEvent) {
    var event = document.createEvent('MouseEvents');
    event.initEvent('click', true, true);
    pom.dispatchEvent(event);
}
else {
    pom.click();
}