Override function in javascript

you can do
xmlHttpReqPost.onerror = function_name_here;

or you can declare your function while assigning
xmlHttpReqPost.onerror = function(){ alert('An error occured'); };

The followinf is an example for overriding the built in alert function:

<script type="text/javascript">
<!--
    window.alert('This is the default alert');
    function overrided(msg)
    {
        confirm(msg);
    }
    window.alert = overrided;
    window.alert('This is the overrided one');
//-->
</script>

Kind Regards
Bakr

basically i had overridden a function like onerror like this....now i want to give new definition of onerror i.e override old definition....

just re-assign it in your object, for example:

var obj = new MyClass();
obj.onerror = function_name;
// re-assign it
obj.onerror = function(){ };

Kind Regards
Bakr

it doesn't work....its calling the old definition?