javascript - Building an HTML table on the fly using jQuery

Question

Below is the code I use to build an HTML table on the fly (using JSON data received from the server).

I display an animated pleasewait (.gif) graphic while the data is loading. However, the graphic freezes while the JavaScript function is building the table. At first, I was just happy to make this happen (display the table), I guess now I need to work on efficiency. At the very least I need to stop the animated graphic from freezing. I can go to a static "Loading" display, but I would rather make this method work.

Suggestions for my pleasewait display? And efficiency? Possibly a better way to build the table? Or maybe not a table, but some other "table" like display

var t = eval( "(" + request + ")" ) ;
var myTable = '' ;
myTable += '<table id="myTable" cellspacing=0 cellpadding=2 border=1>' ;
myTable +=  "<thead>" ;
myTable +=   "<tr>";
for (var i = 0; i < t.hdrs.length; i++) {
    myTable +=    "<th>"     + header +       "</th>";
}
myTable +=   "</tr>" ;
myTable +=  "</thead>" ;
myTable +=  "<tbody>" ;

for (var i = 0; i < t.data.length; i++) {
    myTable +=    '<tr>';
    for (var j = 0; j < t.hdrs.length; j++) {
        myTable += '<td>';
        if (t.data[i][t.hdrs[j]] == "") {
            myTable += "&nbsp;" ;
        }
        else {
            myTable += t.data[i][t.hdrs[j]] ;
        }
        myTable += "</td>";
    }
    myTable +=    "</tr>";
}
myTable +=  "</tbody>" ;
myTable += "</table>" ;

$("#result").append(myTable) ;
$("#PleaseWaitGraphic").addClass("hide");
$(".rslt").removeClass("hide") ;

Answer 1

You basically want to set up your loops so they yield to other threads every so often. Here is some example code from this article on the topic of running CPU intensive operations without freezing your UI:

function doSomething (progressFn [, additional arguments]) {
    // Initialize a few things here...
    (function () {
        // Do a little bit of work here...
        if (continuation condition) {
            // Inform the application of the progress
            progressFn(value, total);
            // Process next chunk
            setTimeout(arguments.callee, 0);
        }
    })();
}

As far as simplifying the production of HTML in your script, if you're using jQuery, you might give my Simple Templates plug-in a try. It tidies up the process by cutting down drastically on the number of concatenations you have to do. It performs pretty well, too after I recently did some refactoring that resulted in a pretty big speed increase. Here's an example (without doing all of the work for you!):

var t = eval('(' + request + ')') ;
var templates = {
    tr : '<tr>#{row}</tr>',
    th : '<th>#{header}</th>',
    td : '<td>#{cell}</td>'
};
var table = '<table><thead><tr>';
$.each(t.hdrs, function (key, val) {
    table += $.tmpl(templates.th, {header: val});
});
...