Javascript Runtime error

Question

why i am getting runtime error in javascript at

var ClientID = document.getElementById("ClientIDTextBox").value;

and my code is:

<script type="text/javascript">
    var ClientID = document.getElementById("ClientIDTextBox").value;
    if (ClientID == "") {
        alert("Please enter ClientID")
      }
</script>

please help me

Let me guess, you put this script before the element you're trying to get the ID of? — Mike Robinson
– Mike Robinson, Commented Sep 21, 2011 at 16:23

JaredPar · Accepted Answer · 2011-09-21 16:23:13Z

3

You are likely getting a runtime error because the call document.getElementById is returning null. The attempt to get the property value on null leads to an error.

Try the following instead

var element = document.getElementById('ClientIDTextBox');
if (element) {
  var ClientID = element.value;
  ...
}

The root cause though is likely that your javascript is running before the DOM is loaded and hence your element with id ClientIDTextBox is not available. Ensure your javascript runs after the DOM is loaded to prevent this problem.

answered Sep 21, 2011 at 16:23

JaredPar

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2 Comments

khr055 Over a year ago

Any logical reason why this is a bad answer? Why the downvote?

JaredPar Over a year ago

@Mike, my first version had getElementById returning undefined instead of null on error. I've since corrected that but it could be the cause of the original downvote.

mothmonsterman · Accepted Answer · 2011-09-21 16:24:52Z

1

<script type="text/javascript">
    var ClientID = document.getElementById("ClientIDTextBox");
    if (ClientID == null || ClientID.value == "") {
        alert("Please enter ClientID")
      }
</script>

answered Sep 21, 2011 at 16:24

mothmonsterman

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