实现按钮触发时间后，60秒之后可重新触发事件，并提供按钮60秒倒计时.
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
var i = 60;
function timeChange() {
document.getElementById("getCheckNum").value ="免费获取验证码("+i+")";
if (i > 0) {
i--;
}
else {
$("getCheckNum").disabled = true; //可用
}
window.setTimeout(function () { timeChange() }, 1000);
}
</script>
</head>
<body>
<input type="button" onclick="timeChange();" id = "getCheckNum" value="获取验证码"/>
</body>
</html>
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