can i use the following code in javascript for validation

function name()
       {
           var a;
           a = document.form1.TextBox1.value;
           for (i = 0; i < a.length; i++)
           {
               if (a.indexof(charCodeAt(i) > 48) != -1 && a.indexof(charCodeAt(i) < 58) != -1)
                {
                   alert("please enter valid name");
               }

           }
       }
       function phno()
       {
       var b;
       b = document.form1.TextBox4.value;
       if (b.charAt(0) == 57 && b.charAt(1) == 56)
       {
       alert("This number is acceptable");
       }
       else if (b.charAt(0) == 57 && b.charAt(1) == 55)
       alert("this number is acceptable");

   }