Run JavaScript from vb.net code behind

Question

I am trying to run some JavaScript from an event handler. Here is my code:

Protected Sub RecordBottomGridRow(ByVal sender As Object, ByVal e As EventArgs) Handles GridView_Body.PageIndexChanging
    Dim scriptText As New StringBuilder()
    scriptText.Append("<script type=""text/javascript"">")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("function RecordBottomGridRow() {")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("var elements = document.getElementsByClassName('exp');")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("var expIndex;")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("for (var i = 0, im = elements.length; im > i; i++) {")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("var elementId = elements[i].id;")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("expIndex = elementId.substring(3);")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("}")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("var fundCode = document.getElementById('htmlFund' + expIndex);")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("var e = document.getElementById('exp' + expIndex);")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("document.getElementById('lastFundChosen') = fundcode.value;")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("document.getElementById('expOrColl').value = e.value;")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("alert(e.value);")
    scriptText.Append(Environment.NewLine)
    scriptText.Append("} </script>")

    ScriptManager.RegisterStartupScript(Me, Me.GetType(), "RecordBottomGridRow", scriptText.ToString(), False)
End Sub

Notice the "alert" at the end there. I run the code and the event fires, but no alert window pops up suggesting the JavaScript code did not run. What am I doing wrong?

How does your javascript code look like in web browser? You can debug javascript code in browser. — yW0K5o
– yW0K5o, Commented Oct 27, 2014 at 17:55
Hit f12 after the page loads and debug the javascript, would be my first suggestion, fyi chrome is easier to debug in than IE — QBM5
– QBM5, Commented Oct 27, 2014 at 17:59
@user3715441 Did you call JavaScript function RecordBottomGridRow? — yW0K5o
– yW0K5o, Commented Oct 27, 2014 at 18:04
I tried in IE and Chrome. I see the script on the page but when I put a break point in and trigger the event the break point never gets reached. — user3715441
– user3715441, Commented Oct 27, 2014 at 18:09
@user3715441 - RegisterStartupScript() will execute the code given to it. Your code, though, only creates a function. It never actually calls anything. Therefore, your function is never actually called. — Justin Niessner
– Justin Niessner, Commented Oct 27, 2014 at 18:21

Comfortably Numb · Accepted Answer · 2014-10-27 20:21:24Z

1

You code just declares function, in essence it just adds to your page output:

function RecordBottomGridRow() {
.....
}

You need to add client-side code that actually call this function by name:

RecordBottomGridRow();

So in your case you can just replace line

scriptText.Append("} </script>")

with (to follow your format):

scriptText.Append("}")
scriptText.Append(Environment.NewLine)
scriptText.Append("RecordBottomGridRow(); </script>")

This code block finishes function declaration with "}" and then adds the call to function to actually execute it on client.

answered Oct 27, 2014 at 20:21

Comfortably Numb

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