Javascript Integer validation

//Javascript----------

function IsInteger(e)
{
var KeyChar = e.keyCode;
// Enter
if(KeyChar != 13)
if(KeyChar > 47 && KeyChar <=58)
return true;
else
return false;
else
return true;
}

//Server side Code

textbox1.Attributes.Add("onKeypress","javascript: return IsInteger(event);");