Calling JavaScript from ASP.NET Master Page and Content Pages - Part I
Calling JavaScript from Master and Content Pages confuses a lot of developers. In this article, we will see some common problems and their solutions of calling JavaScript from a Master/Content page. This article is Part I of the two part series and will cover JavaScript in Master Pages. The next article will cover JavaScript in Content pages.
Call JavaScript From Master Page
You can call an existing JavaScript function from a Master Page or can create one on the fly. Here are some common scenarios:
1. Create a JavaScript function on the fly and call the JavaScript function in the MasterPage Page_Load() event
C#
protected void Page_Load(object sender, EventArgs e)
{
string someScript = "";
someScript = "<script language='javascript'>alert('Called from CodeBehind');</script>";
Page.ClientScript.RegisterStartupScript(this.GetType(), "onload", someScript);
}
VB.NET
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim someScript As String = ""
someScript = "<script language='javascript'>alert('Called from CodeBehind');</script>"
Page.ClientScript.RegisterStartupScript(Me.GetType(), "onload", someScript)
End Sub
The Page.ClientScript.RegisterStartupScript() allows you to emit client-side script blocks from code behind. More info can be found over here http://msdn.microsoft.com/en-us/library/system.web.ui.clientscriptmanager.registerstartupscript.aspx
2. Call an existing JavaScript function on MasterPage Page_Load() event
Let us assume you have an existing JavaScript function declared in between the <head> tags, then here’s how to call that function from Page_Load()
<head runat="server">
<title></title>
<script type="text/javascript">
function invokeMeMaster() {
alert('I was invoked from Master');
}
</script>
<asp:ContentPlaceHolder id="head" runat="server">
</asp:ContentPlaceHolder>
</head>
C#
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.ClientScript.IsStartupScriptRegistered("alert"))
{
Page.ClientScript.RegisterStartupScript
(this.GetType(), "alert", "invokeMeMaster();", true);
}
}
VB.NET
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If (Not Page.ClientScript.IsStartupScriptRegistered("alert")) Then
Page.ClientScript.RegisterStartupScript(Me.GetType(), "alert", "invokeMeMaster();", True)
End If
End Sub
3. Call JavaScript function from MasterPage on Button click
If you want to call a JavaScript function on a Button click, then here’s how to do so:
<head runat="server">
<title></title>
<script type="text/javascript">
function invokeMeMaster() {
}
</script>
<asp:ContentPlaceHolder id="head" runat="server">
</asp:ContentPlaceHolder>
</head>
In the <body> tag, add a Button and use the OnClientClick to call this function
<asp:Button ID="btnMaster" runat="server" Text="Button" OnClientClick="return invokeMeMaster();"/>
The OnClientClick() is called before the postback occurs. This gives us a place to check for some condition and cancel the submit if the condition is not satisfied. We will see an example in Tip 6.
4. Access a control on the MasterPage using JavaScript
If you have a control on the MasterPage and need to access it using JavaScript, then here’s how to do so. In this sample, we will test the length of the TextBox to see if there are 5 or more letters. If the number of letters is less than 5, the form submit will be cancelled.
Add a TextBox and a Button control in the MasterPage (outside the ContentPlaceHolder) as shown below
<body>
<form id="form1" runat="server">
<div>
<asp:Panel ID="panelMaster" GroupingText="MasterPage controls" runat="server">
<asp:TextBox ID="txtMaster" runat="server"></asp:TextBox>
<asp:Button ID="btnMaster" runat="server" Text="Button" OnClientClick="return accessMasterControl();" />
<br />
</asp:Panel>
<asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
In the <head> element of the MasterPage, add the following code:
<head runat="server">
<title></title>
<script type="text/javascript">
function accessMasterControl() {
if (document.getElementById('<%=txtMaster.ClientID%>').value.length <= 5) {
alert('Minimum 5 characters required')
return false;
}
else { return true;}
}
</script>
<asp:ContentPlaceHolder id="head" runat="server">
</asp:ContentPlaceHolder>
</head>
5. Access a control on the Content Page from a MasterPage using JavaScript
If you have a control on the Content Page which has to be accessed in the MasterPage using JavaScript, then here’s how to do so:
On the Content Page, create a TextBox as shown below :
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:Panel ID="panelContent" GroupingText="ContentPage Controls" runat="server">
<asp:TextBox ID="txtContent" runat="server"></asp:TextBox>
</asp:Panel>
</asp:Content>
Now access and populate the TextBox ‘txtContent’ from the MasterPage
<head runat="server">
<title></title>
<script type="text/javascript">
function accessControlContentPage() {
var txtCont = document.getElementById('<%= Page.Master.FindControl("ContentPlaceHolder1").FindControl("txtContent").ClientID %>');
txtCont.value = "I got populated using Master Page";
}
</script>
<asp:ContentPlaceHolder id="head" runat="server">
</asp:ContentPlaceHolder>
</head>
6. Ask user before submitting the form on a MasterPage
In order to ask the user for a confirmation before submitting the form, you can either use code behind or can use simple mark up as shown below:
Declare a Button control that causes postback and write the following code in MasterPage.master.cs or .vb
C#
protected void Page_Load(object sender, EventArgs e)
{
string myScript = @"<script type='text/javascript'>
function askBeforeSubmit() {
var msg = 'Are you sure?';
return confirm(msg);
}
</script>";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "MakeSure", myScript);
form1.Attributes.Add("onsubmit", "return askBeforeSubmit();");
}
VB.NET
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
Dim myScript As String = "<script type='text/javascript'>" & ControlChars.CrLf & " function askBeforeSubmit() {" & ControlChars.CrLf & " var msg = 'Are you sure?';" & ControlChars.CrLf & " return confirm(msg);" & ControlChars.CrLf & " }" & ControlChars.CrLf & " </script>"
Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "MakeSure", myScript)
form1.Attributes.Add("onsubmit", "return askBeforeSubmit();")
End Sub
If you want to avoid a code-behind approach, you can ask the user for a confirmation by using the OnClientClick() on the Submit button
<asp:Button ID="btnMaster" runat="server" Text="Button"
OnClientClick="return confirm('Are you sure?');"/>
I hope you liked the article and I thank you for viewing it.