结合目前所学，简单完成学习作业....

//            var sum=a+b;
//            var ji=a*b;
//            var consult=a/b;
//            var dif=a-b;
//            return [sum,ji,consult,dif];
//        }
//        document.write("a,b的和、积、商、差分别为："+counter(5,2));    

//         判断用户输入的字符是否含有特殊字符

            function judgeChar(ch,specialChars){

                var arr=ch.split("");//将数组切割成一个数组
                var len=arr.length;//获取数组arr的长度
                var specialLen=specialChars.length;//获取数组specialChars的长度
                
                 for(var i=0;i<len;++i){//循环用户输入的字符串
                     for(var j=0;j<specialLen;++j){//循环特殊字符串数组
                         if(arr[i]===specialChars[j]){//进行用户输入的字符与特殊字符比较
                             return false;
                         }
                     }
                 }
                 return true;
            }
            var chars=window.prompt("请输入用户名！");//用户输入字符串
            var specialChars=[
            "#","*","/","<",">",".","(",")","!","?","$","%","（","）","，",",",
            "[","]",";","‘",":"];
                if(judgeChar(chars,specialChars)){//对函数的返回值进行判断
                    alert("用户名合法！");
                }else{
                    alert("抱歉，该用户名含有非法字符！");
                }