IP验证

function isIP(str) { 
    var IP = '(25[0-5]|2[0-4]\d|1\d\d|\d\d|\d)';
    var IPdot = IP + '\.';
    var isIPaddress = new RegExp('^' + IPdot + IPdot + IPdot + IP + '$');   
    return (isIPaddress.test(str));
}