telerikReportViewer exception when preview a report item

[Spyros]

Hello,

I have obtained a trial license for Telerik Reports and have downloaded version 2025.Q2. I have created a sample solution in which the issue I am facing is reproduced. More specifically, I create a report, and when I try to preview the report, the following error appears in the console:

Uncaught (in promise) TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))
    at Array.from (<anonymous>)
    at ParametersArea.allParametersAutoRefresh (telerikReportViewer-19.1.25.521.js:5141:26)
    at ParametersArea.showPreviewButton (telerikReportViewer-19.1.25.521.js:5138:12)
    at w.<anonymous> (telerikReportViewer-19.1.25.521.js:5396:13)
    at w.<anonymous> (telerikReportViewer-19.1.25.521.js:374:43)
    at Generator.next (<anonymous>)
    at o2 (telerikReportViewer-19.1.25.521.js:25:20)

This issue occurs whether I use Kendo UI in combination with Telerik Reports or only Telerik Reports, according to the information described in your knowledge base.

Could you please check this, as I am interested in purchasing a subscription for both the Reports and Kendo UI?

[Petar]

Hello Spyros,

I believe I answered your concern in the private ticket 1688944. However, I will also share my response here in the forum thread, as it may be helpful to other customers who encounter the same issue.

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TypeError: undefined is not iterable

The error occurs due to a breaking change introduced in the latest version, where the report viewer is no longer fully initialized immediately after the `$("#content").telerik_ReportViewer` call. Therefore, the reportViewer.reportSource call right after the initialization of the report viewer does not behave as expected. This change was not intended, and we will investigate it further to find a resolution. In the meantime, I recommend using the ready event of the report viewer, as this is when the report viewer is fully initialized:

    function getReport() {
        $("#content")
            .telerik_ReportViewer({
                serviceUrl: "api/reports",
                viewMode: telerikReportViewer.ViewModes.PRINT_PREVIEW,
                scaleMode: telerikReportViewer.ScaleModes.SPECIFIC,
                scale: 1,
                enableAccessibility: false,
                sendEmail: { enabled: false },

                pageReady: function (e, args) {
                    $("#telerikReportModalContainer").resize();
                },

                ready: function (e, args) {
                    let reportViewer = $("#content").data("telerik_ReportViewer");

                    if (reportViewer !== undefined) {
                        reportViewer.reportSource({
                            report: 'Report1',
                            parameters: {
                                Parameter1: "hello world"
                            },
                        });

                        reportViewer.refreshReport();
                    }
                }
            });
    }

Broken UI

In addition to the client-side error, I also noticed that the user interface of the page is broken, as it misses essential styles required for the correct appearance. For example, a reference to a Kendo UI theme is required for this:

    <link rel="stylesheet" href="https://kendo.cdn.telerik.com/themes/10.2.0/default/default-ocean-blue.css" />
    <style>
        #content {
            position: relative;
            height: 1000px;
            width: 1000px;
        }
    </style>

The additional styles added can be adjusted based on your preferences. You may also choose to use a different Kendo UI theme.

Wrapping up

I hope this helps. If you continue to experience any issues even after applying the above changes, please let me know, and I will be happy to assist you further.

Regards,
Petar
Progress Telerik