Question

Here is my code :

function search_buddy() 
{
    $.post("num.php",function (ret){
        num=ret;
    });
    $("#Layer7").html(num);
}
</script>

<div id="Layer8">
     Find a buddy : 
    <input type="text" id="search" onkeyup="search_buddy()"/>&nbsp;:
</div>

Now,when i enter one character into the text box with id=search, the function search_buddy doesn’t seem to get triggered. Whereas, if i enter two characters or more,the function works perfectly.Why is this happening ?

Answer 1

Best resource on DOM events: http://www.quirksmode.org/dom/events/keys.html

It looks like your event handler “search_buddy” fires an AJAX request, which is asynchronous. The rest of the function runs in parallel with the AJAX request, so “num” is undefined before the $.post returns.

// num is undefined here... unless your network has 0 latency
$("#Layer7").html(num);

You need to wrap this code (pasted above) in a callback function. It appears to be parameter number 3:
http://api.jquery.com/jQuery.post/

Untested, but best guess:

function search_buddy() {
    $.post("num.php", function (ret) {
        num=ret;
        $("#Layer7").html(num);
    });
}

Here are some modifications to help you understand:

function search_buddy() {
    alert("before the $.post execution");
    $.post("num.php", function (ret) {
        num=ret;
        $("#Layer7").html(num);
        alert("$.post callback");
    });
    alert("immediately after the $.post execution");
}

Note: “alert” will halt all JavaScript processing so you will be able to see what events occur when.