function WordCount() {
    var wordsallowed = 300;
    var inp = document.getElementById('txtabstract').value;

    var regex = /\s+/gi;
    var wordcount = jQuery.trim(inp).replace(regex, ' ').split(' ').length;
    if (wordcount <= wordsallowed) {
        chars = inp.length;
    } else {
        var text = inp.val();
        var new_text = text.substr(0, chars);
        document.getElementById('txtabstract').value=new_text;
        wordcount--;
    }
    $("#labelcount").html(wordcount);
}

http://www.classgist.com

Javascript code for counting the number of words in a sentence. It can be used to allow only a certain number of words.

JavaScript Word Count

JavaScript