如何使用 JavaScript 强制执行 HTML 文本区域的最大长度？

<textarea onkeypress="return imposeMaxLength(event, this, 110);" rows="4" cols="50"></textarea>

<script>
  function imposeMaxLength(event, object, maxLength) {
    return (object.value.length <= maxLength) || (event.keyCode == 8 || event.keyCode == 46 || (event.keyCode >= 35 && event.keyCode <= 40));
  }
</script>

window.onload = function() {
  var txts = document.getElementsByTagName('TEXTAREA');

  for (var i = 0, l = txts.length; i < l; i++) {
    if (/^[0-9]+$/.test(txts[i].getAttribute("maxlength"))) {
      var func = function() {
        var len = parseInt(this.getAttribute("maxlength"), 10);

        if (this.value.length > len) {
          alert('Maximum length exceeded: ' + len);
          this.value = this.value.substr(0, len);
          return false;
        }
      }

      txts[i].onkeyup = func;
      txts[i].onblur = func;
    }
  }
};