How to remove words after particular counting of words using jquery?

I have one text area in which i want to allow only 30 words and remove remaining extra words.

$("#short_desc").keydown(function(e){

    var d = $(this).val().split(/\b[\s,\.-:;]*/).length;
    if(d > 30){
        alert("Only 30 words allowed");
        e.preventDefault();
        // here i want to add logic how to remove words.
        return false;
    }
});

I have tried with character count but cant short out this logic can some one provide some hint. I have one logic that count spaces and then count character count till 30 spaces and get sub string before that character count.