Salesforce - Mass update records with onclick javascript

{!REQUIRESCRIPT("/soap/ajax/35.0/connection.js")} 
 var records = {!GETRECORDIDS($ObjectType.Account)}; 
 var updateRecords = []; 
 if (records[0] == null) 
 { 
  alert("Please select at least one Account") 
 } 
 else 
 { 
  for (var i=0; i<records.length; i++) 
  { 
   var acc = new sforce.SObject("Account"); 
   acc.id = records[i]; 
   acc.Type = "Customer"; 
   updateRecords.push(acc); 
  } 
  result = sforce.connection.update(updateRecords); 
  window.location.href = "/001"; 
 }