js 实时监听textarea输入

html:

<textarea class="area" name="" id="text1" maxlength="100" oninput="checkTxt()"></textarea>
<p class="notice">已输入<span id="num">0</span>个字</p>

js:

function checkTxt() {
    var obj = $('#text1'),
        len = obj.val().length;
    $('#num').html(len);
}