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Thread: Javascript performance is IE

  1. #1
    Join Date
    Oct 2008
    Posts
    13

    Javascript performance is IE

    Hi,

    I've got the code below which i'm using to highlight a table column on mouse over, it works perfectly in firefox but in IE6/7/8 it is extremely slow. Is there anyway I can optimise it to improve IE performance? I have heard that getElementById is inherently slow in IE.

    Thanks

    function highlight(col,color)
    {
    var tot = document.getElementById("rowcount").value;
    for(i=1; i<=tot-1; i++)
    document.getElementById(col+i).style.backgroundColor=color;
    }

    function unhighlight(col)
    {
    var tot = document.getElementById("rowcount").value;
    for(i=1; i<=tot-1; i++)
    document.getElementById(col+i).style.backgroundColor="";
    }

  2. #2
    Join Date
    Dec 2003
    Location
    Bucharest, ROMANIA
    Posts
    15,428
    like this?
    Code:
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
    <html>
    <head>
    <title>untitled</title>
    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
    <meta http-equiv="Content-Style-Type" content="text/css">
    <meta http-equiv="Content-Script-Type" content="text/javascript">
    <style type="text/css">
    #myTable td{
    background:#ccc;
    }
    #myTable td.tdon{
    background:#ff0000;
    }
    #myTable td.tdoff{
    background:#ccc;
    }
    </style>
    <script type="text/javascript">
    function addRoll(){
    var allTD=document.getElementById('myTable').getElementsByTagName('td'), i=0, td;
    while(td=allTD[i++]){
    td.onmouseover=rollOn;
    td.onmouseout=rollOff;
    }
    }
    function rollOn(){
    var allTD=this.parentNode.parentNode.getElementsByTagName('td'), i=0, td;
    while(td=allTD[i++]){
    td.className=td.cellIndex==this.cellIndex?'tdon':'tdoff';
    }
    }
    function rollOff(){
    var allTD=this.parentNode.parentNode.getElementsByTagName('td'), i=0, td;
    while(td=allTD[i++]){
    td.className='tdoff';
    }
    }
    onload=addRoll;
    </script>
    </head>
    <body>
    <table width="200" border="0" id="myTable">
      <tr>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </table>
    
    </body>
    </html>
    Last edited by Kor; 03-16-2009 at 10:47 AM.

  3. #3
    Join Date
    Feb 2006
    Posts
    2,930
    you can set the background color of a column of cells with one statement, if you have a colgroup for each column you want to be able to change.

    colgroups are declared before any rows, tbodies, theads or tfoots.

    Code:
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
    <html lang="en">
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>HTML Table Colgroups</title>
    
    <!-- code for testing only -->
    <script type= "text/javascript" >
    function colBg(e){
        var e= window.event || e;
        var who= e.target || e.srcElement;
        if(who.nodeName== 'TH' || who.nodeName== 'TD'){
            var index= 0, pa= who.parentNode.getElementsByTagName('*');
            while(index< pa.length && pa[index]!= who)++index;
            who= document.getElementById('col'+(++index));
            var arg= prompt('Enter color value','#ffdead');
            who.style.backgroundColor= arg;  
        }  
    }
    
    onload= function(){
        document.getElementsByTagName('table')[0].ondblclick= colBg;
    }
    </script>
    </head>
    
    <body>
    <h1>HTML Table Columns</h1>
    <h2>Double Click a cell to change its column background</h2>
    <div>
    <table border="1" width="50&#37;" >
    <caption>Three Column Table</caption>
    <colgroup id="col1" span="1"></colgroup>
    <colgroup id="col2" span="1"></colgroup>
    <colgroup id="col3" span="1"></colgroup>
    
    
    <thead class="sortableClass">
    <tr><th>Make</th><th>Model</th><th>Price</th></tr>
    </thead>
    <tbody>
    <tr><td>Ford</td><td>Truck</td><td>$23,000</td></tr>
    <tr><td>Subaru</td><td>Wagon</td><td>$21,000</td></tr>
    <tr><td>Kia</td><td>Compact</td><td>$13,000</td></tr>
    <tr><td>Lexus</td><td>Sedan</td><td>$35,000</td></tr>
    <tr><td>Honda</td><td>SUV</td><td>$26,000</td></tr>
    
    </tbody>
    </table>
    </div>
    
    </body>
    </html>
    Last edited by mrhoo; 03-16-2009 at 11:55 AM.

  4. #4
    Join Date
    Dec 2003
    Location
    Bucharest, ROMANIA
    Posts
    15,428
    Good idea with the colgroup, mrhoo. But even in this case you don't need the ids for the colgroups; you still can use the order of the colgroups in their collection and the cellIndex property of the cells. Should work faster.

  5. #5
    Join Date
    Feb 2006
    Posts
    2,930
    Code:
    you still can use the order of the colgroups in their collection and the cellIndex
    Good point, Kor- the fewest possible specific ids in any code, the better.
    Last edited by mrhoo; 03-17-2009 at 08:20 AM.

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