CODEWITHSUNDEEP
javascripthtmlgetelementbyid
pasta
pasta

Reputation: 1476

Javascript: document.getElementById() returns NULL

I am quite new with Javascript and I got a problem with document.getElementById() that always returns NULL, and that's driving me nuts.

I have a element in my code and I want to get its coordinates so I can move it.

Here is the code:

<html>
  <head>
    <script type="text/javascript" >
      function MoveIt(obj) {
        alert(obj); // returns "Object HTMLDivElement"
        var xx = document.getElementById("arect");

        if(document.getElementById("arect").value == null) {
          alert('NULL >> ' + xx.value);
        }
        else {
          alert('NOT NULL >>' + xx.value);
        }

        posX = xx.style.scrollTop;
        posY = xx.style.left;
      }
    </script>
  </head>

  <body bgcolor="white" >
    <DIV class="background" id="MyDiv2">  
      <div id="arect" name="arect" class="transbox" onmousedown="MoveIt(this);" >
      </div>
    </div>
  </body>
</html>

The above function MoveIt() always returns NULL

Upvotes: 15

Views: 104216

Answers (6)

Sailab Rahi
Sailab Rahi

Reputation: 600

The page contents need to be loaded before trying to read them. Try 

window.onload = function() {
  // run your script in here
}

Or if you're using jQuery, prefer

$(document).ready(function() {
  ...
}

Upvotes: 32

Dogugun Ozkaya
Dogugun Ozkaya

Reputation: 134

in my case it was because of having this line at the beginning of the jsp/html(whatever) file:

<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">

removing it solved my problem.

Upvotes: -1

Vijender Reddy
Vijender Reddy

Reputation: 1

if the button is set to visisble= false then you cannot get the id of that button on client side. To hide the button use

button1.Style.Add("display","none")-- for visible false

and

button1.Style.Add("display","block")-- for visible true

and even if button is enabled false we cannot get the Id of the button on client side

You can get the id of the button by document.getElementById('<%= button1.ClientID %>'); Or if you set the ClientIDMode="Static" for the control in aspx page you can get it directly by document.getElementById('button1'); Or document.getElementById('MainContent_button1');--- MainContent here is the Id of the contentplaceholder if you have the id of the contenet placeholder different use that id_button1.

Upvotes: -1

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385154

You never checked getElementById(...) for NULL.

You checked getElementById(...).value for NULL, and divs don't have a "value".

Also note that you forgot to close that <div /> tag, which is illegal in your XHTML... and used an SVG doctype for some reason. SVG is not HTML.

It's not really clear what you're trying to do here.

Upvotes: 8

MNIK
MNIK

Reputation: 1619

if(document.getElementById("arect").value == null){
    alert('NULL >> '+ xx.value);
  }

This code always returns null or error. If you want to see if the object exists, do the following....

if(xx == null)
   alert('Object does not exist');
else 
   alert('Object exists. Inner HTML: ' + xx.innerHTML);

Also, div does not have value. If you want to get the html inside div, use xx.innerHTML

Upvotes: 3

Pointy
Pointy

Reputation: 413717

The "arect" element is a <div>, and <div> elements don't have a "value".

Get rid of that bogus SVG doctype too.

Upvotes: 8

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