How to print table using Javascript?

Here is your code in a jsfiddle example. I have tested it and it looks fine.

http://jsfiddle.net/dimshik/9DbEP/4/

I used a simple table, maybe you are missing some CSS on your new page that was created with JavaScript.

<table border="1" cellpadding="3" id="printTable">
    <tbody><tr>
        <th>First Name</th>
        <th>Last Name</th>      
        <th>Points</th>
    </tr>
    <tr>
        <td>Jill</td>
        <td>Smith</td>      
        <td>50</td>
    </tr>
    <tr>
        <td>Eve</td>
        <td>Jackson</td>        
        <td>94</td>
    </tr>
    <tr>
        <td>John</td>
        <td>Doe</td>        
        <td>80</td>
    </tr>
    <tr>
        <td>Adam</td>
        <td>Johnson</td>        
        <td>67</td>
    </tr>
</tbody></table>

One cheeky solution :

  function printDiv(divID) {
        //Get the HTML of div
        var divElements = document.getElementById(divID).innerHTML;
        //Get the HTML of whole page
        var oldPage = document.body.innerHTML;
        //Reset the page's HTML with div's HTML only
        document.body.innerHTML = 
          "<html><head><title></title></head><body>" + 
          divElements + "</body>";
        //Print Page
        window.print();
        //Restore orignal HTML
        document.body.innerHTML = oldPage;

    }

HTML :

<form id="form1" runat="server">
    <div id="printablediv" style="width: 100%; background-color: Blue; height: 200px">
        Print me I am in 1st Div
    </div>
    <div id="donotprintdiv" style="width: 100%; background-color: Gray; height: 200px">
        I am not going to print
    </div>
    <input type="button" value="Print 1st Div" onclick="javascript:printDiv('printablediv')" />
</form>