Question

I have the below chunk of code. I’ve debugged through and located the snippet that is causing a long delay in IE6.

Basically the code loops through a document converting it to XML and sending to a PDF. On Ubuntu and Firefox 4 it takes 3 seconds. On IE it can take up to 40 seconds regularly.

/**
* This function builds up the XML to be saved to the DM.
*/
function getXMLToSave(){

var text="<workbook><sheet><name>Adv4New</name>";

//show_props(document.adv4.row10col1, "document.adv4.row10col1");

for(i=1;i<157;i++){
    text = text + "<row number='" + i + "'>";
    for(j=1;j<=7;j++){
        text = text + "<col ";
        //alert(eval('document.adv4.row'+i+'col'+j+'.readonly'));
        try{
            text = text + "number='" + j + "' label='" + eval('document.adv4.row'+i+'col'+j+'.className')+ "'";
        }
        catch (e) {
            text = text + "number='" + j + "' label=''";
        }
        try {
            if(eval('document.adv4.row'+i+'col'+j).readOnly)
            text = text + " type='readonly'";
            else
            text = text + " type=''";
        }
        catch (e) {
            text = text + " type=''";
        }
        try {
            text = text + " color='" + eval('document.adv4.row'+i+'col'+j+'.style.color') + "'";
        }
        catch (e) {
            text = text + " color=''";
        }
        text = text + ">";
        try {
            // don't wrap in a CDATA (like previously), but run cleanNode
            // this fixes html entities
            var content = eval('document.adv4.row'+i+'col'+j+'.value');
            text = text + cleanNode(content);
        }
        catch (e) {
            text = text + "0";
        }
        text = text + "</col>";
    }
    text = text + "</row>";
}
text = text + "</sheet></workbook>";

return text;

}

I believe its the eval function causing the delay in IE6. Is there a neat solution to fix this. Thanks very much

Answer 1

It’s likely that it’s all the string concatentation that makes it slow. Each time you add something to the text, it will copy all the previous text into a new string.

Newer browsers have optimised code for this special case, so for them the impact is less.

Instead of concatenating strings like this:

text = text + "something";

use an array instead:

var text = [];

then add items to the array using the push method:

text.push("<workbook><sheet><name>Adv4New</name>");

Finally just join the strings together:

return text.join('');