如何在javascript中添加显示div的条件

Question

I tried adding condition in Javascript for div show:hide in HTML5

#demo {
    width: 500px;
    height: 500px;
    background-color: lightblue;
    display: none; 
}

Insert value between 0-9 to set function

<input id="num" type="text" name="txt1">
<button onclick="myFunction()">Check</button> 
<div id="demo">This is my Demo element.</div>
<div id="qwe"></div>

<script>
function myFunction() {
  var num;
  num = document.getElementById("num").value;
   if (a < 10) {
    document.getElementById("demo").style.display = "inline"; }
    else { document.getElementById("qwe").innerHTML = "Not a Valid Number"; 
   }
}
</script>

Am I wrong in the condition part

Answer 1

You used undefined variable "a"

if (a < 10) {

you have to change it to:

if (num < 10) {

try this code:

 <input id="num" type="text" name="txt1"> <button onclick="myFunction()">Check</button> <div id="demo">This is my Demo element.</div> <div id="qwe"></div> <script> function myFunction() { var num; num = document.getElementById("num").value; if (num < 10) { document.getElementById("demo").style.display = "inline"; document.getElementById("qwe").innerHTML = ""; } else { document.getElementById("qwe").innerHTML = "Not a Valid Number"; document.getElementById("demo").style.display = "none"; } } </script>