Pseudo Code

recursive_ajax.js

var dataresults;

function getResults(restURL) {
  $.ajax({
    url: restUrl,
    type: 'GET',
    dataType: 'JSON',
    headers: {
      "accept":"application/json;odata=verbose",
      "X-RequestDigest": $("#__REQUESTDIGEST").val()
    },
    success: funcation(data) {
    dataresults = dataresults.concat(data)
      if(data.__next){
        getResults(data.__next);
    }
  });
}

// do something with dataresults