In both JavaScript and VB.NET, it is important to note that the expression does not yield a value

Question

In both JavaScript and VB.NET, it is important to note that the expression does not yield a value

Within the Create View for the "Deal" model, I have implemented a JavaScript function that is intended to generate a new object within a List Property when a specific button is clicked.

The error message "expression does not produce a value" has appeared. I am confused by this as I do not require a value; my objective is simply to create an empty object within the list.

Specifically, the line in the JavaScript of my view which adds the new Period to the list is triggering the error:

<script type="text/javascript">
    function addRow() {
        @Model.Periods.Add(New DealPeriod());
        ...
    }
</script>

Details of the "Deal" Model:

Public MustInherit Class Deal

    ...

    <Display(name:="Periodos")>
    Public Property Periods As New List(Of DealPeriod)

javascript .net vb.net

Answer 1

Answer №1

Addressing two key issues here which are crucial for resolving the problem mentioned in the question regarding "expression does not produce a value":

When you see the @ symbol in this context, it signifies to "output the result of the following to the http response stream".

Since List.Add() does not return a value (void), there is no data to send to the response stream, resulting in that particular error message.

In simpler terms, the @ requires a value, and List.Add() doesn't provide one.

The second issue highlighted here suggests a potential mix-up between server-side execution and client-side execution (not to be confused with server-side/client-side code, which can coexist as demonstrated). It seems like an attempt to add a new "DealPeriod" when "addRow" is triggered - but that's not how it functions. VB.Net code operates on the server side, while JavaScript code runs on the client side (the browser), operating independently from each other.

To establish a connection between them, options such as using an ajax call or signalr can be explored.

Answer 2

Addressing two key issues here which are crucial for resolving the problem mentioned in the question regarding "expression does not produce a value":

When you see the @ symbol in this context, it signifies to "output the result of the following to the http response stream".

Since List.Add() does not return a value (void), there is no data to send to the response stream, resulting in that particular error message.

In simpler terms, the @ requires a value, and List.Add() doesn't provide one.

The second issue highlighted here suggests a potential mix-up between server-side execution and client-side execution (not to be confused with server-side/client-side code, which can coexist as demonstrated). It seems like an attempt to add a new "DealPeriod" when "addRow" is triggered - but that's not how it functions. VB.Net code operates on the server side, while JavaScript code runs on the client side (the browser), operating independently from each other.

To establish a connection between them, options such as using an ajax call or signalr can be explored.

Answer 3

Answer №2

When you expect

@Model.Periods.Add(New DealPeriod());

to be executed upon calling the javascript function, it doesn't actually happen as expected. This is because the inline VB code runs on the server-side before the HTML is sent to the client. To see the rendered code in that javascript function, open your webpage and view its page source. You will notice that the specific line of code is not included. Instead, what you should do is make an ajax call to a controller that will handle the desired logic.

Answer 4

When you expect

@Model.Periods.Add(New DealPeriod());

to be executed upon calling the javascript function, it doesn't actually happen as expected. This is because the inline VB code runs on the server-side before the HTML is sent to the client. To see the rendered code in that javascript function, open your webpage and view its page source. You will notice that the specific line of code is not included. Instead, what you should do is make an ajax call to a controller that will handle the desired logic.

In both JavaScript and VB.NET, it is important to note that the expression does not yield a value

Answer №1

Answer №2

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