Don't fire Javascript in Sharepoint 2013

I have got a script which count users in a group:

<script>
var userCollection;
function start(){
var clientContext = new SP.ClientContext();
//Get all groups in site
var groupCollection = clientContext.get_web().get_siteGroups();
// Get the group by name
group = groupCollection.getByName('Sharepoint Group');
//Get all SP Users in SP Group
 userCollection = group.get_users();
clientContext.load(userCollection);  
//Execute Query
clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded1), Function.createDelegate(this, this.onQueryFailed)); 
}

function onQuerySucceeded1() {
    alert('Liczba użytkowników w grupie PROFlash wynosi:  ' +userCollection.get_count());
    document.getElementById("count").innerHTML=userCollection.get_count();
}

function onQueryFailed(sender, args) {
    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

</script>

I tried everything, but it fire me only when I Editing a site, or adding to a site, orremove new user:

<asp:Content ID="Main" ContentPlaceHolderID="PlaceHolderMain" runat="server">
<script type="text/ecmascript" language="ecmascript">

var user;
var FlashGroup;

function runCode() {

     var clientContext = new SP.ClientContext();
     var groupCollection = clientContext.get_web().get_siteGroups();

     FlashGroup = groupCollection.getByName('Sharepoint Group');
     user = clientContext.get_web().get_currentUser();
     var userCollection = FlashGroup.get_users();
     userCollection.addUser(user);

     clientContext.load(user);
     clientContext.load(FlashGroup);
     clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceededZapisz), Function.createDelegate(this, this.onQueryFailed));

}

function onQuerySucceededZapisz() {
    alert(user.get_title() + " został dodany do " + FlashGroup.get_title());
start();
}

function onQueryFailed(sender, args) {
    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
start();
}

</script>

    <input id="Button11" type="button" class="ZapiszGrupaPROFlash" value="Zapisz mnie do grupy" onclick="runCode()" />

</asp:Content>

I dont know why I can't use it on page after put start() on page. Please help me.