[JS]

Get Field Names from SP List.js

$.ajax({
  async: false,
  url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists(guid'listID')/fields?$top=1000",
  method: "GET",
  headers: {
    Accept: "application/json; odata=verbose",
  },
  success: function (data) {
    var colStr = [];
    var elements = {};
    $.each(data.d.results, function (i, val) {
      var title = val.Title;
      var internalName = val.InternalName;      
      elements[internalName] = { title: title, name: internalName, form: "{{" + internalName + "}}" };
    });
    
    console.log(JSON.stringify(elements));
  },
  fail: function (jqXHR, status, error) {
    console.log(error);
  },
});