下拉框选中项 · JavaScript

## 随机选中下拉框 ``` <body> <input type="button" id="btn" value="设置"> <select name="" id="select"> <option value="">1</option> <option value="">2</option> <option value="">3</option> </select> <script> var btn = document.getElementById('btn'); btn.onclick = function () { var select = document.getElementById('select'); var options = select.getElementsByTagName('option'); var random = Math.floor(Math.random() * options.length); var option = options[random]; option.selected = true; } </script> ```