//сохранение как картинки
document.getElementById('save_as_picture').addEventListener('click', save_picture);

function save_picture(){
  html2canvas(document.getElementById('field')).then(function(canvas) {
    var my_screen = canvas;
    var dataURL = my_screen.toDataURL("image/jpeg");
    var link = document.createElement("a");
    document.body.appendChild(link);
    link.href = dataURL;
    let my_file_name = prompt('Enter picture name');
    link.download = my_file_name + ".jpg";
    link.click();
    document.body.removeChild(link);
  });
}