<button onclick="download('11.txt', 'fsdfdsfsdfsdfsdfsdfsf')">下载</button>

function download(filename, content) {
    var aLink = document.createElement('a')
    var blob = new Blob([content])
    var event = new MouseEvent('click', {
      'view': window,
      'bubbles': true, //是否冒泡
      'cancelable': true //事件是否可以取消
    });
    aLink.download = filename
    aLink.href = URL.createObjectURL(blob)
    aLink.dispatchEvent(event)
}