<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml"><head> ???<title>My Practice</title> ???<script src="jquery-3.2.1.js"></script></head><body> ???<div> ???????<textarea onkeyup="javascript:checkWord(this);" onmousedown="" ></textarea>(<span id="ResidueCount">10</span>) ???</div> ???<span>test</span> ???<script type="text/javascript"> ???????var str = ""; ???????var maxLength = 10; ???????function checkWord(c) { ???????????str = c.value; ???????????//console.log(str + " ???" + str.length); ???????????var len = maxLength - str.length; ???????????if (len >= 0) { ???????????????$("#ResidueCount").text(len); ???????????} ???????????else { ???????????????c.value = str.substring(0, maxLength); ???????????} ???????} ???</script></body></html>参考：http://www.studyofnet.com/news/529.html
JS实现文字倒计数
原文地址：http://www.cnblogs.com/cat66/p/7774164.html