Unable to pass simple array of strings to ASP.NET controller with ajax

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I have an ASP.NET Core 8 view with a script that collects Id's from a table of checkboxes. The script collects them correctly into an arrayOfFeatureIds. I have checked the values in the console and they are correct. The JavaScript I am working with is:

JavaScript

@section scripts {
    <script>
        document.getElementById('updateMap').addEventListener('click', () => {
            var arrayOfFeatureIds = [];
            var selected;
            $("#features tbody tr").each(function () {
                selected = 
                    $(this).find("input[type='checkbox']:checked").val();
                if (selected) {
                    arrayOfFeatureIds.push($(this)
                        .find("input[type='hidden']").val());
                }
            });
            console.log(arrayOfFeatureIds); // THIS IS CORRECT
            passData = JSON.stringify(this.arrayOfFeatureIds);
            $.ajax({
                url: "/Maps/UpdateMap",
                type: "POST",
                data: passData,
                contentType: 'application/json',
                dataType: "json",
                success: function () {
                    alert("OK");
                },
                error: function (errMsg) {
                    alert(errMsg);
                }
            });
        });
    </script>
}

The script successfully POSTs back to the Controller. The Controller code is:

C#

[HttpPost]
public JsonResult UpdateMap(string[] ids)
{
    return Json("Success");
}

However, the string[] is always empty. I have tried multiple ways to send it in the JavaScript, but no luck. Can anybody let me know where I'm going wrong?

What I have tried:

I've tried multiple ways to stringify the array:

1. data: JSON.stringify(arrayOfFeatureIds)
2. passData = JSON.stringify(arrayOfFeatureIds)
3. passData = JSON.stringify(this.arrayOfFeatureIds)

I've also gone through several articles and tried the solutions on this site, but no luck.

Posted 9-Jul-24 5:15am

RobertHitchins

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Richard Deeming · Accepted Answer · 2024-07-09T05:47:00

Quote:

JavaScript

var arrayOfFeatureIds = []; // Declare a local variable
...
arrayOfFeatureIds.push(...); // Push values into the local variable
...
console.log(arrayOfFeatureIds); // Log the local variable

passData = JSON.stringify(this.arrayOfFeatureIds); // Use an undefined property from the global namespace!

Remove this. from the JSON.stringify line. You're referring to a completely different, and most likely undefined, object.

Quote:

C#

[HttpPost]
public JsonResult UpdateMap(string[] ids)
{
    return Json("Success");
}

You may need to add [FromBody] to the parameter; I suspect it's trying to bind the values from the query-string instead.

C#

[HttpPost]
public JsonResult UpdateMap([FromBody] string[] ids)