Run javascript method in asp.net webforms method

Question

I want to show a javascript alert when a user changes a value in a select-box. This is my code, what am i doing wrong?

aspx

<asp:DropDownList ID="ddlGroups" AutoPostBack="true" runat="server" OnSelectedIndexChanged="ddlWagons_SelectedIndexChanged"></asp:DropDownList>

aspx.cs

    protected void ddlWagons_SelectedIndexChanged(object sender, EventArgs e)
    {
        ClientScriptManager script = Page.ClientScript;
        script.RegisterStartupScript(this.GetType(), "OpenWindowScript", "alert('Clicked')");
    }

I belive you can achieve this result by using jQuery.

andrey.shedko
– andrey.shedko

2014-11-18 09:42:36 +00:00
Commented Nov 18, 2014 at 9:42 — andrey.shedko
– andrey.shedko, Commented Nov 18, 2014 at 9:42
I don't want to use jQuery

Lord Vermillion
– Lord Vermillion

2014-11-18 09:42:54 +00:00
Commented Nov 18, 2014 at 9:42 — Lord Vermillion
– Lord Vermillion, Commented Nov 18, 2014 at 9:42

Anik Islam Abhi · Accepted Answer · 2014-11-18 09:47:38Z

2

try this

Add

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
</asp:ScriptManager>

to your designer part

and in code part add

var ID="Whatever the data is";
ClientScript.RegisterStartupScript(this.GetType(), "script", "alert('"+ID+"');", true);

If you are using update panel

try this

var ID="Whatever the data is";
ScriptManager.RegisterStartupScript(this, this.GetType(), "script", "alert('"+ID+"');", true);

answered Nov 18, 2014 at 9:47

Anik Islam Abhi

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Comments

James · Accepted Answer · 2014-11-18 09:44:40Z

2

You should be able to handle the onchange event before the postback occurs

<asp:DropDownList runat="server" onchange="alert('Clicked')" />

If you don't need a postback then don't use a server control.

answered Nov 18, 2014 at 9:44

James

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3 Comments

Lord Vermillion Over a year ago

I forgot to mention that i also want to call a javascript method when the backend method has completed, is this possible?

James Over a year ago

@TobiasOlofsson so you need the postback? Are you running something at the server-side and then need to callback into the client?

yogi970 Over a year ago

@TobiasOlofsson after back end code completes you can use RegisterStartupScript for adding a script.

artm · Accepted Answer · 2014-11-18 09:45:40Z

2

Have you tried

<asp:DropDownList ID="ddlGroups" AutoPostBack="true" runat="server" OnSelectedIndexChanged="ddlWagons_SelectedIndexChanged" clientIdMode="static"></asp:DropDownList>

and in JS:

document.getElementById("ddlGroups").addEventListener("change", function(){
    alert("new value: " + this.options[this.selectedIndex].value);
});

answered Nov 18, 2014 at 9:45

artm

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4 Comments

Lord Vermillion Over a year ago

I forgot to mention that i also want to call a javascript method when the backend method has completed, is this possible?

artm Over a year ago

You mean an alert? Have you looked into ajax calls?

Lord Vermillion Over a year ago

Uncaught TypeError: Cannot read property 'addEventListener' of null

artm Over a year ago

Have you used clientIdMode="static"?

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