Limit text area value and cut the rest

I have a textarea which users can enter some tags. I need to limit 开发者_如何学运维this tags to 20 tags.

Tags could be enterer this way

maytag1,mytag2,mytag3

What i wrote is this function

function limitTags()
{

    var tags        =   $("input[type=text][name=tags]").val()
    var tag         =   $.trim(tags);
    var selected            = new Array();

    /**
     * replace the last ','
     */
    if(tag.substring(tag.length - 1) == ",")
    {
         *///tag = tag.replace(tag.length - 1, '');
    }


    var enteredTags = tag.split(",");

    if( enteredTags.length > 20 )
    {
        //$("input[type=text][name=tags]").val(enteredTags.join(",", enteredTags));

        alert("Only 20 Tags allowed");
    }


}

The alert works just fine but, after the alert box is gone. i can continiue entering tags till the alert box appears.

What i need is cut the text after the messagebox which was entered also the last ","

I hope i could ask my question clear.

Thanks

You can use the slice method to cut the array down to 20 entries before setting the value:

$("input[type=text][name=tags]").val(enteredTags.slice(0,20).join(","));

See: https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/Slice

Intercept "," pressing, and check how many entries the user inserted so far. If he's trying to insert too many entries just prevent further insertions.

$('input[type=text][name=tags]').keyup(function(e) {
    if((e.keyCode == 188) && ($(this).val().split(",").length > 19)) {
        alert('Only 20 Tags allowed');
    }
});