# CallBackStart

Learn the syntax and arguments for the CallBackStart event available in Spread for ASP.NET.

## Content

Occurs just before the Spread component makes a request to the ASPX page.

## Syntax

[Inline HTML]

```html
<ELEMENT CallBackStart = "handler" ...>
```

[JavaScript]

```javascript
FpSpread1.addEventListener("CallBackStart", handler, ...)
```

or

```javascript
FpSpread1.onCallBackStart = handler
```

## Arguments

***event.cancel***
Whether to cancel the callback request
***event.async***
Asynchronous or not
***event.command***
Command name of the callback

## Return Type

None

## Remarks

This event is triggered when there is a request to the ASPX page.
If the cancel argument is set to true, the request is canceled.

## Example

This example JavaScript code maps the event for the Spread on the client side. Set ClientAutoCalculation to True for the Spread component in Page Load and type in a cell at run time to see the alerts in the client side code.

```javascript
<script lang="javascript" type="text/javascript">
window.onload = function () {
var spread1 = document.getElementById("<%=FpSpread1.ClientID %>");
if (document.all) {
// IE
   if (spread1.addEventListener) {
     // IE9
     spread1.addEventListener("CallBackStart", CallBackStart, false);
     spread1.addEventListener("CallBackStopped", CallBackStopped, false);
      } else {
     // Other versions of IE and IE9 quirks mode (no doctype set)
      spread1.onCallBackStart = CallBackStart;
      spread1.onCallBackStopped = CallBackStopped;
      }
}
      else {
      // Firefox
      spread1.addEventListener("CallBackStart", CallBackStart, false);
      spread1.addEventListener("CallBackStopped", CallBackStopped, false);
     }
   }
    
   function CallBackStart(event) {
     if (event==null) event = window.event;
        alert("start");
     }
   
   function CallBackStopped(event) {
      alert("stop");
   }
</script>
```

## See Also

[CallBackStopped](/spreadnet/docs/latest/online-asp/overview/spweb-clientscriptref/clientscript-members/clientscript-allevents/CSSR-onCallBackStop)
[Scripting Members](/spreadnet/docs/latest/online-asp/overview/spweb-clientscriptref/clientscript-members)