jQuery中未检测到输入

This does not fire the code, and I'm not sure why. I've tried .change, .on('input'), everything I can find. The problem is likely simple. What is wrong?

$(function() {
    alert('hie');
    //the min chars for username  
    var min_chars = 3;

    //result texts  
    var characters_error = 'Minimum amount of chars is 3';
    var checking_html = 'Checking...';

    //when button is clicked  
    $('#myusername').bind("change paste keyup", function() {
        //run the character number check  
        if ($('#myusername').val().length < min_chars) {
            //if it's bellow the minimum show characters_error text                 
            $('#username_availability_result').html(characters_error);
            $('#checkuser').show(fast);
            alert('hsdi');
        }
        else {
            //else show the cheking_text and run the function to check  
            $('#username_availability_result').html(checking_html);
            $('#checkuser').show(fast);
            check_availability();
            alert('hi');
        }
    });
});

//function to check username availability
function check_availability() {

    //get the username  
    var username = $('#myusername').val();
    //use ajax to run the check  
    $.post("../php/checkuser.php", {username: username},
    function(result) {
        //if the result is 1  
        if (result == 1) {
            //show that the username is available  
            $('#username_availability_result').html(username + ' is Available');
        } else {
            //show that the username is NOT available  
            $('#username_availability_result').html(username + ' is not Available');
        }
    });
}

HTML

<tr>
    <td>Username</td>
    <td><input type="text" name="username" placeholder="Username"  id="myusername"></td>
</tr>  
<tr id="checkuser" style="display: none">
    <td>

    </td>
</tr>

check this sample. I just removed the "fast" parameter from your .show() call.

http://jsfiddle.net/juaning/PsvS7/

From those to calls, let me know if that fix your problem.

$('#checkuser').show(fast);alert('hsdi');

$('#checkuser').show(fast);

Not 100% sure what you're problem is, there is some missing HTML to go along with your code.

But, there is an error in your js, you need to surround fast with quotes.

$('#checkuser').show('fast');

$('#checkuser').show('fast');

That will at least get your alerts to show up.