Passing arguments to JavaScript function from code-behind

Asked 25/4, 2009 at 6:16 Answered 24/3, 2013 at 16:7

Solved c#javascript .net asp.net code-behind

I would like to call a javascript function from an aspx control. For instance, suppose I had:

<html xmlns="http://www.w3.org/1999/xhtml">
    <head runat="server">
<title>Untitled Page</title>
<script type="text/javascript">
    function test(x, y)
    {

    }
</script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Button ID="Button1" runat="server" Text="Button"
         onclick="Button1_Click"/>
    </div>
    </form>
</body>
</html>

and in the code behind:

protected void Button1_Click(object sender, EventArgs e)
{
    // do stuff (really going to a database to fill x and y)
    int[] x = new int[] { 1, 2, 3, 4, 5 };
    int[] y = new int[] { 1, 2, 3, 4, 5 };

    // call javascript function as test(x,y);
}

Is there a way to do it?

Disable answered 25/4, 2009 at 6:16 Comment(1)

This question is similar, but not quite the same. In my question, I am being more specific about how to pass arguments to the javascript function, and supplying example code. I'm interested in the specific mechanics of it. – Disable 25/4, 2009 at 15:46

You can use the Page.ClientScript.RegisterStartupScript method.

Ampersand answered 25/4, 2009 at 6:23 Comment(1)

How does it work? I need to call a JavaScript function from codebehind without any parameters, but I don't see how to use this :S – Makebelieve 25/11, 2011 at 12:52

Look at the ScriptManager.RegisterStartupScript method if you're using a ScriptManager or any Ajax controls/asynchronous postbacks.

Edit:

Actually, the function you want is probably ScriptManager.RegisterClientScriptBlock

Gordon answered 25/4, 2009 at 6:22 Comment(0)

You can use the Page.ClientScript.RegisterStartupScript method.

Ampersand answered 25/4, 2009 at 6:23 Comment(1)

How does it work? I need to call a JavaScript function from codebehind without any parameters, but I don't see how to use this :S – Makebelieve 25/11, 2011 at 12:52

Some other things I found out:

You can't directly pass in an array like:

this.Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "xx",   
"<script>test("+x+","+y+");</script>");

because that calls the ToString() methods of x and y, which returns "System.Int32[]", and obviously Javascript can't use that. I had to pass in the arrays as strings, like "[1,2,3,4,5]", so I wrote a helper method to do the conversion.

Also, there is a difference between this.Page.ClientScript.RegisterStartupScript() and this.Page.ClientScript.RegisterClientScriptBlock() - the former places the script at the bottom of the page, which I need in order to be able to access the controls (like with document.getElementByID). RegisterClientScriptBlock() is executed before the tags are rendered, so I actually get a Javascript error if I use that method.

http://www.wrox.com/WileyCDA/Section/Manipulating-ASP-NET-Pages-and-Server-Controls-with-JavaScript.id-310803.html covers the difference between the two pretty well.

Here's the complete example I came up with:

// code behind
protected void Button1_Click(object sender, EventArgs e)
{
    int[] x = new int[] { 1, 2, 3, 4, 5 };
    int[] y = new int[] { 1, 2, 3, 4, 5 };

    string xStr = getArrayString(x); // converts {1,2,3,4,5} to [1,2,3,4,5]
    string yStr = getArrayString(y);

    string script = String.Format("test({0},{1})", xStr, yStr);
    this.Page.ClientScript.RegisterStartupScript(this.GetType(),
    "testFunction", script, true);
    //this.Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
    //"testFunction", script, true); // different result
}
private string getArrayString(int[] array)
{
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < array.Length; i++)
    {
        sb.Append(array[i] + ",");
    }
    string arrayStr = string.Format("[{0}]", sb.ToString().TrimEnd(','));
    return arrayStr;
}

//aspx page
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
    <script type="text/javascript">
    function test(x, y)
    {
        var text1 = document.getElementById("text1")
        for(var i = 0; i<x.length; i++)
        {
            text1.innerText += x[i]; // prints 12345
        }
        text1.innerText += "\ny: " + y; // prints y: 1,2,3,4,5

    }

    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Button ID="Button1" runat="server" Text="Button"
         onclick="Button1_Click" />
    </div>
    <div id ="text1"> 
    </div>
    </form>
</body>
</html>

Disable answered 26/4, 2009 at 5:8 Comment(1)

If you want to pass objects/arrays to your clientside javascript, you could look into ASP.NET & JSON (using a hiddenfield in your HTML). A good tutorial on ASP.NET & JSON is here: blogs.msdn.com/rakkimk/archive/2009/01/30/… – Overthecounter 29/4, 2009 at 14:2

include script manager

code behind function

ScriptManager.RegisterStartupScript(this, this.GetType(), "HideConfirmBox", "javascript:HideAAConfirmBox(); ", true);

Fridell answered 29/4, 2011 at 8:11 Comment(0)

Response.Write("<scrip" + "t>test(" + x + "," + y + ");</script>");

breaking up the script keyword because VStudio / asp.net compiler doesn't like it

Melmon answered 25/4, 2009 at 6:38 Comment(0)

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Call java script function on Code behind</title>
    <script  type="text/javascript">
    function abc()
    {
        var a=20;
        var b=30;
        alert("you enter"+a+":"+b);
    }
    </script>
</head>

cs code

protected void Page_Load(object sender, EventArgs e)
{
    TextBox2.Attributes.Add("onkeypress", "return abc();");
}

try this

Cryptograph answered 9/1, 2011 at 5:23 Comment(0)

I think you want to execute the javascript serverside and not in the browser after post-back, right?

That's not possible as far as I know

If you just want to get it execute after postback, you can do something like this:

this.Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "xx", "<script>test("+x+","+y+");</script>");

Lysias answered 25/4, 2009 at 6:35 Comment(3)

I am looking for client side execution after post back, sorry for not being more clear. So with this methodology, this would call an existing script on the page, correct? – Disable 25/4, 2009 at 15:47

yes a javascript function called "test" will be executed immediatly after postback. This is useful for showing alert popups to the user. from googling: "ClientScript.RegisterClientScriptBlock is used to make sure a specific script is included in the header part of the page. The type and key parameters helps ensure that a given script is included only once even if RegisterClientScriptBlock is called multiple time for the same script (provided the same type and key)." – Lysias 25/4, 2009 at 17:22

I seem to have posted the wrong method before. You need "RegisterClientScriptBlock". (I edited it in my post) – Lysias 25/4, 2009 at 17:23

If you are interested in processing Javascript on the server, there is a new open source library called Jint that allows you to execute server side Javascript. Basically it is a Javascript interpreter written in C#. I have been testing it and so far it looks quite promising.

Here's the description from the site:

Differences with other script engines:

Jint is different as it doesn't use CodeDomProvider technique which is using compilation under the hood and thus leads to memory leaks as the compiled assemblies can't be unloaded. Moreover, using this technique prevents using dynamically types variables the way JavaScript does, allowing more flexibility in your scripts. On the opposite, Jint embeds it's own parsing logic, and really interprets the scripts. Jint uses the famous ANTLR (http://www.antlr.org) library for this purpose. As it uses Javascript as its language you don't have to learn a new language, it has proven to be very powerful for scripting purposes, and you can use several text editors for syntax checking.

Twit answered 10/6, 2010 at 10:10 Comment(0)

 <head>
    <script type="text/javascript">

        function test(x, y) 
        {
            var cc = "";
            for (var i = 0; i < x.length; i++) 
            {
                cc += x[i]; 
            }
            cc += "\ny: " + y; 
            return cc;
        }

    </script>



</head>

<body>

    <form id="form1" runat="server">

        <asp:Button ID="Button1" runat="server" Text="Button"   />

        <p>
             <asp:TextBox ID="TextBox1"  Name="TextBox1"  runat="server" AutoPostBack="True"  TextMode="MultiLine"></asp:TextBox>
        </p>



    </form>
</body>

protected void Page_Load(object sender, EventArgs e)
{
    int[] x = new int[] { 1, 2, 3, 4, 5 };
    int[] y = new int[] { 1, 2, 3, 4, 5 };

    string xStr = getArrayString(x); // converts {1,2,3,4,5} to [1,2,3,4,5]
    string yStr = getArrayString(y);

    string script = String.Format(" var y = test({0},{1}) ; ", xStr, yStr);
    script += String.Format("  document.getElementById(\"TextBox1\").value = y  ");

    this.Page.ClientScript.RegisterStartupScript(this.GetType(),  "testFunction", script, true);
  //  this.Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "testFunction", script, true); // different result
}




private string getArrayString(int[] array)
{
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < array.Length; i++)
    {
        sb.Append(array[i] + ",");
    }
    string arrayStr = string.Format("[{0}]", sb.ToString().TrimEnd(','));
    return arrayStr;
}

Dolomites answered 24/3, 2013 at 16:7 Comment(0)

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