tryjsref_number_placeholder2 在线代码实例

 <input type="number" id="myNumber" placeholder="Favorite Number">
<p>点击按钮显示 number 字段的提示信息。</p>
<button onclick="myFunction()">点我</button>
<p id="demo"></p>
<script>
function myFunction() {
    var x = document.getElementById("myNumber").placeholder;
    document.getElementById("demo").innerHTML = x;
}
</script>