1。CSDN 是依靠 CSS 方式禁止复制的。反制方法很简单，加条 CSS 样式就行了：pre, code {user-select: auto !important;}
2。针对CSDN，强烈推荐这个油猴脚本！
https://greasyfork.org/scripts/378351-%E6%8C%81%E7%BB%AD%E6%9B%B4%E6%96%B0-csdn%E5%B9%BF%E5%91%8A%E5%AE%8C%E5%85%A8%E8%BF%87%E6%BB%A4-%E4%BA%BA%E6%80%A7%E5%8C%96%E8%84%9A%E6%9C%AC%E4%BC%98%E5%8C%96-%E4%B8%8D%E7%94%A8%E5%86%8D%E7%99%BB%E5%BD%95%E4%BA%86-%E8%AE%A9%E4%BD%A0%E4%BD%93%E9%AA%8C%E4%BB%A4%E4%BA%BA%E6%83%8A%E5%96%9C%E7%9A%84%E5%B4%AD%E6%96%B0csdn/code/%F0%9F%94%A5%E6%8C%81%E7%BB%AD%E6%9B%B4%E6%96%B0%F0%9F%94%A5%20CSDN%E5%B9%BF%E5%91%8A%E5%AE%8C%E5%85%A8%E8%BF%87%E6%BB%A4%E3%80%81%E4%BA%BA%E6%80%A7%E5%8C%96%E8%84%9A%E6%9C%AC%E4%BC%98%E5%8C%96%EF%BC%9A%F0%9F%86%95%20%E4%B8%8D%E7%94%A8%E5%86%8D%E7%99%BB%E5%BD%95%E4%BA%86%EF%BC%81%E8%AE%A9%E4%BD%A0%E4%BD%93%E9%AA%8C%E4%BB%A4%E4%BA%BA%E6%83%8A%E5%96%9C%E7%9A%84%E5%B4%AD%E6%96%B0CSDN%E3%80%82.user.js