文本框输入字数限制JQuery

<textarea cols="20" rows="8" id="shareContent" name="shareContent" onkeyup="words_deal()" style=" width:600px; height:100px; resize:none;"></textarea>

function words_deal() {

var curLength = $("#pushContent").val().length;

if (curLength > 140) {

var num = $("#pushContent").val().substr(0, 140);

$("#pushContent").val(num);

alert("输入字符不能超过140");

}

else {

$("#limitTip").text("您还可以输入的字符为：" + (140 - $("#pushContent").val().length));

}

}