I'm trying to send arrays as post variables in an Ajax call using formData. For some reason they are getting converted to strings when I look in the console. I can't update the functions accepting the data to accept strings, they must accept arrays. I was reading about using the serialize function but then I'm also left with strings...so I'm not sure how to do this. Here is the code I have so far:

function submitSearch(method) {

  if (method==='ajax_getPrograms') {
      fields = ['pkProgramID','fldName','fldOrganization','fldProgramStartDate','fldProgramEndDate'];
  }
  if (method==='ajax_getPlots') {
      fields = ['id','lat','long','plotSampleYear'];      
  }  
  if (method==='ajax_getTrees') {
      fields = ['id','species','DBH','treeStatus','treeSampleYear'];      
  }   
  var posturl = baseURL + "data/"+method;
  var formData = new FormData();

  formData.append('fields',fields);

  $.ajax({
            url: posturl,
            cache: false,
            data: formData,
            method: 'POST',
            mimeType: "multipart/form-data",
            contentType: false,
            processData: false,
            type: 'POST',
            error: function (xhr, status, error) {
                console.log(xhr);
                console.log(status);
                console.log(error);
            },
            success: function (data) {
 
                console.log(data);

            }
        });
}

When I submit that I get an error that my function is receiving a string and not an array, and this is what I see in the network tab of the console:

Any help is appreciated, thank you!