<!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
原文：http://www.cnblogs.com/cat66/p/7774164.html