clipboard

https://cdn.bootcss.com/clipboard.js/2.0.4/clipboard.min.js
npm install clipboard --save

<input id="foo" value="被复制内容">
    <button class="btn"  data-clipboard-target="#foo">
        复制
    </button>

<button class="btn"  data-clipboard-text="内容">
        复制
    </button>

var clipboard = new clipboard('.btn');
clipboard.on('success', function(e) {
    alert("复制成功")
});