call clientside javascript from asp.net c# page

Question

I have a c# asp.net page and an update function which will update the database. In this function I would like to call some client side javascript. I've read a lot about registering a start up script in page_load() but this is always trigger on page load (funny that!)

How would I register then call a script inside my update function? Triggered when a user clicks the "update" button. I have tried the following (inside my function)

protected void doUpdate(object sender, EventArgs e) {

    string jScript;
    jScript = "<script type=text/javascript>alert('hello');<" + "/script>";

    ClientScript.RegisterStartupScript(GetType(), "Javascript", jScript);
}

but it isn't fired. Any ideas? Many thanks.

[update]

It's now working - the function looks like this

protected void doUpdate(object sender, EventArgs e) {
    ScriptManager.RegisterStartupScript(this, GetType(),"Javascript", "cleanup();",true);
}

Cleanup() is the javascript function in my HTML. Thanks for the help guys :)

Is the control causing the postback inside an UpdatePanel?

Claudio Redi
– Claudio Redi

2012-03-16 12:27:46 +00:00
Commented Mar 16, 2012 at 12:27 — Claudio Redi
– Claudio Redi, Commented Mar 16, 2012 at 12:27
yes it is. Is that the likely problem?

Matt Facer
– Matt Facer

2012-03-16 12:35:30 +00:00
Commented Mar 16, 2012 at 12:35 — Matt Facer
– Matt Facer, Commented Mar 16, 2012 at 12:35
Added an answer. Yes, that's likely the problem :)

Claudio Redi
– Claudio Redi

2012-03-16 12:45:18 +00:00
Commented Mar 16, 2012 at 12:45 — Claudio Redi
– Claudio Redi, Commented Mar 16, 2012 at 12:45

Claudio Redi · Accepted Answer · 2012-03-16 12:38:08Z

3

If the control causing the postback is inside an UpdatePanel you need to use

ScriptManager.RegisterStartupScript

answered Mar 16, 2012 at 12:38

Claudio Redi

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2 Comments

Matt Facer Over a year ago

so would that be in the page load?

Claudio Redi Over a year ago

you can use it on doUpdate, that's fine

Shelakel · Accepted Answer · 2012-03-16 12:31:01Z

1

You can't 'execute' client side scripts from the web server (the client knows who the server is, but not the other way around).

The only way to overcome this limitation is by a. create a long-polling process that requests something from the server, the server doesn't complete the request till it has something to return (then client side it makes another request).

What you are really looking for is websocket (duplex) enabled communication. You can check out alchemy websockets or SignalR (has a pretty nice library with dynamic proxy generation).

The reason why that 'script always works on Page_Load' is because it effectively injects your script tag into the html returned for the page requested.

answered Mar 16, 2012 at 12:31

Shelakel

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Comments

Mike Guthrie · Accepted Answer · 2012-03-16 12:43:57Z

1

Your Update button is likely using the standard ASP Button behavior, meaning it is type="submit" when it is rendered. Since that's the case, you can just use:

Page.ClientScript.RegisterOnSubmitStatement

Keep in mind that will register a script for every postback, not just the Update button. So, if you only want some javascript run on clicking Update, you would need to check if the EventTarget is UpdateButton.ClientID. Also, RegisterOnSubmitStatement always adds the <script> tags, so don't include those in the javascript statement.

An even easier solution, the ASP Button itself also has an OnClientClick property. This will run client-side code (javascript) when the button is clicked in the browser.

edited Mar 16, 2012 at 12:43

answered Mar 16, 2012 at 12:35

Mike Guthrie

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2 Comments

Matt Facer Over a year ago

thanks - this seems to be the right option. However I assume it's called onSubmit. I am looking for a way to programatically call the function after my code has done some checks. For example, update was OK - then call the JS.. otherwise dont. Thanks :)

Mike Guthrie Over a year ago

Ah, if you do need the script run after a postback, then I think Claudio's solution is the way you'll need to go.

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