How do I invoke a suitable event on the client?

I have two TextBoxes above a GridView. The GridView is wrapped in an UpdatePanel and both TextBoxes trigger an ajax GridView refresh OnTextChanged.

This is my problem. The user may sometimes leave nothing in a TextBox - when that happens I assume they mean zero, so I want to put the value of '0' back into the TextBox (which the user has removed, by deleting the entire content of the TextBox). See the javascript: restoreTextBox() function below. What event is available for me to do this and can I just invoke the event or do I need to inherit something. I have tried beginRequest() or pageLoaded() but nothing happens.

PS: The txtAssetPc_TextChanged() server-side method is working fine to update the GridView. I just want to know how I can use a suitable client event.

aspx Code only below (the server code is missing as it is not relevant to this problem).

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true">
<Services>
<asp:ServiceReference Path="~/RedirectService.asmx" />
</Services>
</asp:ScriptManager>
<asp:ValidationSummary ID="vsFunds" runat="server" ValidationGroup="TextPC" DisplayMode="BulletList" ShowSummary="true" /><br />
Equities ≥<asp:TextBox ID="txtEquities" runat="server" Text="0" CssClass="text" MaxLength="3" ToolTip="Enter minimum percentage value of Equities (0 - 100)" OnTextChanged="txtAssetPc_TextChanged" AutoPostBack="true" />% <asp:RangeValidator ID="rvEquities" ControlToValidate="txtEquities" runat="server" ErrorMessage="Valid range for Equities is 0-100" Type="Integer" MinimumValue="0" MaximumValue="100" ValidationGroup="TextPC" /><br />
Fixed Income ≥<asp:TextBox ID="txtFixedIncome" runat="server" Text="0" CssClass="text" MaxLength="3" ToolTip="Enter minimum percentage value of Fixed Income (0 - 100)" OnTextChanged="txtAssetPc_TextChanged" AutoPostBack="true" />% <asp:RangeValidator ID="rvFixedIncome" ControlToValidate="txtFixedIncome" runat="server" ErrorMessage="Valid range for Fixed Income is 0-100" Type="Integer" MinimumValue="0" MaximumValue="100" ValidationGroup="TextPC" />

<asp:UpdatePanel ID="upAssetExposure" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:GridView ID="gvAssetExposure" runat="server" AutoGenerateColumns="False" DataKeyNames="PensionFundID"
AllowSorting="True" AllowPaging="True" PageSize="50"
OnRowDataBound="gvAssetExposure_RowDataBound" OnPageIndexChanging="gvAssetExposure_PageIndexChanging" OnSorting="gvAssetExposure_Sorting" >
<PagerSettings Mode="NumericFirstLast" />
<Columns>
<asp:BoundField HeaderStyle-CssClass="ResultsHeading" ItemStyle-CssClass="tdCol32" NullDisplayText="N/A" DataField="FundName" HeaderText="Investor" SortExpression="FundName" />
<asp:BoundField HeaderStyle-CssClass="ResultsHeading" ItemStyle-CssClass="tdCol12" NullDisplayText="N/A" DataField="TotalFundAssetsSterling" HeaderText="Total Fund Assets (GBP)" SortExpression="TotalFundAssetsSterling" DataFormatString="{0:GBP ###,### m; N/A}" HtmlEncode="False" />
<asp:BoundField HeaderStyle-CssClass="ResultsHeading" ItemStyle-CssClass="tdCol12" NullDisplayText="N/A" DataField="Equities_Percent" HeaderText="Equities (%)" SortExpression="Equities_Percent" DataFormatString="{0:##; N/A}" HtmlEncode="False" />
<asp:BoundField HeaderStyle-CssClass="ResultsHeading" ItemStyle-CssClass="tdCol12" NullDisplayText="N/A" DataField="FixedIncome_Percent" HeaderText="Fixed Income (%)" SortExpression="FixedIncome_Percent" DataFormatString="{0:##; N/A}" HtmlEncode="False" />
</Columns>
</asp:GridView>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="txtEquities" EventName="TextChanged" />
<asp:AsyncPostBackTrigger ControlID="txtFixedIncome" EventName="TextChanged" />
</Triggers>
</asp:UpdatePanel>

<script type="text/javascript">
var aTxt = ['<%txtEquities.ClientID%>','<%txtFixedIncome.ClientID%>'];
function restoreTextBox(){
for (var e=0; e < aTxt.length; e++){
var txtBox = document.getElementById(aTxt[e]);
if (txtBox.value == '')
txtBox.value = '0';
}
}
</script>

Just add onblur="restoreTextBox();" to your textboxes.