$('#textbox').keyup(function() {
    var value = $('#textbox').val();
    if(value != ''){
        if(!value.match(/^[5678910]$/))  
            textboxError();
        else{
            var length = value.length;
            if(value.charAt(length-1) == 0 && value.charAt(length-2) != 1)
                textboxError();
        }
    }
};

$('#textbox').change(function() {
    var value = $('#textbox').val();
    if(value != '')
        textboxError();
    }
};

function textboxError(){
    $('#textbox').val(''); 
    $('#textbox').focus(); 
    alert("Please Enter only between 5 and 10 ");
}

What we are doing is,

1. Check if value is empty (If empty don't perform anything)
2. If not empty check if the value matches to defined set
3. If it match, now we do check for 10. What we do is if last entered item of field is 0, than the previous field must be 1 so it makes a 10. If not we throw error.
4. But here is a problem, the user might enter 1 and leave the field without entering another char. So, u can extend this by onchange field.
5. Onchange, now we check for count of 1 and that should match count of 10. It fixes our problem. You don't have to worry of 0 because we already check it in keyup block.

I Didn't check the code. So if any typos or errors, u can replace them.

onkeyup is enabled by default so you do not need to set it to true. If you do, you break the functionality already built into the plugin.

You have three options:

1) Leave the onkeyup option out of .validate(). This keeps onkeyup functionality enabled by default. (edit: "by default" means that validation occurs on every "key-up" event only after the field is initially validated by another event.)

DEMO: http://jsfiddle.net/ZvvTa/

2) onkeyup can be set to false to disable this option.

DEMO: http://jsfiddle.net/ZvvTa/1/

3) Replace onkeyup with your own callback function to modify how it operates. (Demo uses default function)

DEMO: http://jsfiddle.net/ZvvTa/2/

Below is the default, unmodified, onkeyup callback function:

onkeyup: function( element, event ) {
    if ( event.which === 9 && this.elementValue(element) === "" ) {
        return;
    } else if ( element.name in this.submitted || element === this.lastElement ) {
        this.element(element);
    }
}

See: http://docs.jquery.com/Plugins/Validation/validate#toptions

EDIT:

By default, the plugin does not do any "key-up" validation until after the field is initially validated by another event. ("Lazy" validation)

So here is a more properly modified version of the onkeyup callback function that will provide immediate onkeyup validation. ("Eager" validation)

DEMO: http://jsfiddle.net/QfKk7/

onkeyup: function (element, event) {
    if (event.which === 9 && this.elementValue(element) === "") {
        return;
    } else {
        this.element(element);
    }
}

You need to add a \ in front of the d, without it the d is represented as the character d and not a numeric value. Here's the expression you should use ^\d{3,4}$.

EDIT

The first part was on track, but I missed that you were passing the pattern as a string to another function. If you were to run new RegExp('^\d{3,4}$', "") it would work, but because it was being passed through a function, the \ character was being removed. In order to pass a string with a backslash in it, you need to escape the slash with another back slash like so \\. This means your new expression should be ^\\d{3,4}$.

When developing regular expression I usually use something like http://regexpal.com/ to help test them. Keep in mind that for this one you would have to check the ^$ match at line breaks (m) box for it to match multiple tests on multiple lines

Why would you bother using the keyup event? It'd be better off using the keydown or keypress event and then cancelling it (I used this site to find the keycodes):

function ei (event) {
    event = event || window.event;

    switch (event.keyCode) {
        case 47: //.
        case 33: //!
        //etc
            event.preventDefault(); //cancel the current action, which will stop it writing out to the textbox
            break;
        default:
            break;
    }
}

I would also suggest you look into jQuery rather than having inline JavaScript to hook up your events and also take a look at the jQuery Validation plugin as that should help take care of a lot of your code.

I think you can write your SK_sendChatMessage function like below.

function SK_sendChatMessage(text,recipient_id,e) {
document.title = document_title;
textarea_wrapper = $('.chat-textarea');
chat_messages_wrapper = $('.chat-messages');

if (e.keyCode == 13 && e.shiftKey == 0 && text == '') {
    alert('enter text');
}
else{
  textarea_wrapper.find('textarea').val('');
    chat_messages_wrapper.append('<div class="chat-text align-right temp-text" align="right"><div class="text-wrapper float-right">' + text + '<div class="marker-out"><div class="marker-in"></div></div></div><div class="float-clear"></div></div>');

    $.post(SK_source() + '?t=chat&a=send_message', {text: text, recipient_id: recipient_id}, function (data) {
        chat_messages_wrapper
            .append(data.html)
            .scrollTop(chat_messages_wrapper.prop('scrollHeight'))
            .find('.temp-text')
                .remove();
    });
}

I'm guessing "when the last keypress is up" means when the two password fields contain values of the same length? If so, then have the keyup event listener first check the length of the values. For example, don't try to validate until the 2nd password length is equal or longer than the length of the 1st password. Of course, if the 2nd is longer than the first, it fails validation :)

onChange only works on certain types of elements (<SELECT> for e.g.).

onKeyUp will evaluate with every keypress, which is "heavy"

blur() is perhaps better because it is triggered each time you leave a field. But what about when you are still in the field and click the submit button?

Therefore, onsubmit is the best solution -- or a combination of the two. There is no problem with evaluating different ways for different fields, and validating again after clicking submit

Try to use jquery, it will work in each browser

function validate() {  
console.log("validation start");
    var msg;  
    if($("input[name='userPass']").val().length >5)
        console.log("good");//msg="good";  
    else
       console.log("poor");// msg="poor";  
    document.getElementById("mylocation").innerText=msg;  
}