As the results value is an array and the objects within that are comma-delimited, you could do:

let resultReturn = {
  success: true, 
  results: [
      "heading1, head2, head3",
      "string, 200, 1.1",
      "string2, 100, 1.2",
      ]
    }

function loaddata() {
  let r = resultReturn.results;
  let tbody = document.getElementById("datatable");

  for (let i = 0; i < 3; i++) {
    let thisRow = r[i];
    let newRow = "<tr>";
    let thisRowItems = thisRow.split(",");
    for (let j = 0; j < thisRowItems.length; j++) {
      newRow += "<td>" + thisRowItems[j] + "</td>";
    }
    newRow += "</tr>";
    tbody.innerHTML += newRow;
  }
}
window.onload = loaddata;

Note that I’ve wrapped this in a function for testing purposes, so you won’t need to include the window.onload line

So I’ve previously made tables with XML formatted results, and JSON results that are "key: data" formatted, and I would access the data like: results.heading1, and use a map to put the data into a table, matching the key with the data.

A new client can only send their data in the below format, and I’m not sure how to add this into a table on my site when the keys are all in the first row, and not alongside each entry. I’ve done a lot of googling but nothing seems to be matching my circumstances!

How would I go about making a table when the keys(headings) are not alongside the data, but in the first result row instead?

The JSON data in question is shown as below. I make an API call to the client, and the response is in the same format as the example below:

resultReturn: {
  success: true, 
  results: [
      "ID, Name, Age",
      "A1, Bob, 31",
      "B1, John, 24",
      "C2, Doe, 160",
      ,
  resultsHTML: ""
    }