Textarea maxlength with counter

<textarea id="field" onkeyup="countChar(this)"></textarea>
    <div><span  id="charNum">50</span> words remining</div>

function countChar(val) {
        var len = val.value.length;
        if (len >= 50) {
          val.value = val.value.substring(0, 50);
        } else {
          $('#charNum').text(50 - len);
        }
      };