The JSON.stringify function is used to convert a JavaScript object or value into a JSON string. In the provided code:

formData.append('selectedData', JSON.stringify(selectedData));

Here’s why JSON.stringify is used in this context:

FormData Limitation:

FormData is an inbuilt JavaScript object that holds a collection of key/value pairs for the values of form fields. Preparing data for AJAX queries is one of its frequent uses.
FormData is capable of handling basic key/value pairs, but it might struggle with more intricate nested objects or arrays.

Converting Array to String:

The array of selected site names is called selectedData.
This array is transformed to a string using JSON.stringify before being appended to FormData.
The array is represented simply in the JSON string that is produced.

Storing JSON in FormData:

Strings can be handled as values by FormData.
The data structure is preserved when the array is converted to a JSON string, and it is simple to parse the data back into an array on the server side.

Consistent Data Format:

Using JSON.stringify ensures that the data is consistently formatted as a string, making it easier to handle on both the client and server sides.

Easy Parsing on the Server:

When the data is sent to the server, the server can easily parse the JSON string back into a data structure (e.g., an array) using JSON parsing functions.
Here’s a simplified example:

// Client side
var selectedData = ['facebook', 'twitter', 'instagram'];
var formData = new FormData();
formData.append('selectedData', JSON.stringify(selectedData));

// Server side (in PHP, for example)
$selectedData = json_decode($_POST['selectedData']);

By using JSON.stringify on the client side and json_decode on the server side, you ensure a smooth and consistent handling of complex data structures during the data transfer process.

Code Example

function mySocialsClick(button, selectedData) {
    var itemId = button.data('id'); // Get the data-id attribute value
    console.log("Button clicked with data-id:", itemId);

    // Prepare data for the AJAX request
    var formData = new FormData();
    formData.append('itemId', itemId); // Add itemId to formData
    formData.append('selectedData', JSON.stringify(selectedData)); 
    if (selectedData.length === 0) {
        $('#social-modal').modal('show');
    }
    else
    {
    $.ajax({
        url: "{{ route('addcarts.store') }}",
        method: "POST",
        data: formData,
        contentType: false,
        cache: false,
        processData: false,
        dataType: "json",
        headers: {
        'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content') // Add CSRF token if needed
          },
        beforeSend: function () {
            // Add any code to execute before sending the AJAX request
        },
        success: function (data) {
           console.log("addcarts.store aata hain");
           var prices = data.prices;
           var social = data.filters;
        var influencer = data.influencer;
        var publisher = data.publisher; 
        console.log('add prices success click ho rha ha', prices);    
        },
        error: function (xhr, textStatus, errorThrown) {
            // Handle the error response
        }
    });

}
}