I could not manage to work the download attribute when downloading vcards via data URL by Chrome on IOS. I use code below

function download(filename, text) {
        var element = document.createElement('a');
        element.setAttribute('href', 'data:text/vcard;charset=utf-8,' + encodeURIComponent(text));
        element.setAttribute('download', filename);
        element.style.display = 'none';
        document.body.appendChild(element);
        element.click();
        document.body.removeChild(element);
    }

It works fine with Safari on IOS and Chrome on Android. But Chrome on IOS just ignore file name and download file just with name "document" so in not opened by contact app.