jQuery .find() fails to find occasionally

I am trying to parse the HTML of a webpage to DOM by loading it into an iframe and do some searching on the DOM afterwards. Here's the code

function f(callback) {
    var tmp = document.createElement('iframe');
    $(tmp).hide();
    $(tmp).insertAfter($('foo'));
    $(tmp).attr('src', url);

    $(tmp).load(function() {
        var bdy = tmp.contentDocument.body;
        callback(bdy);
        $(tmp).remove();
    });
}

In the callback function if I do something like the following

functi开发者_运维问答on callback(bdy) {
    alert($(bdy).find('bar').length);
}

sometimes it gives me the correct value but sometimes it gives me 0 instead. However, if I do the following it works

var tmp = document.createElement('iframe');
$(tmp).hide();
$(tmp).insertAfter($('foo'));
$(tmp).attr('src', url);

$(tmp).load(function(tmp) {
    setTimeout(function() {
        var bdy = tmp.contentDocument.body;
        callback(bdy);
        $(tmp).remove();
    }, '100');
});

Since setTimeout() depends on the client's end, I would like to know if there is any better way to achieve the same goal. Thanks.

Check this question out, along with its many answers and related questions.

Update; here's some code that waits for #bar to get loaded:

function f(callback) {
    var tmp = document.createElement('iframe'),
        $tmp = $(tmp);
    $tmp.hide()
        .insertAfter($('foo'))
        .attr('src', url);

    $tmp.load(function() {
        var bdy = tmp.contentDocument.body,
            $bdy = $(bdy); // small optimization

        var waitForBar = function() {
            if($bdy.find('#bar').length > 0) {
                callback(bdy);
                $tmp.remove();
            } else
                setTimeout(waitForBar, 50);
        };
        waitForBar();
    });
}