How to parse knack api response

wrote a function to call knack api to request records but I can't find a way to parses the response object 
I tried to use .getContextText() from appscript but it throw error saying it's not a function
function getKnackRecords(objID, filter, sortObj, recordID) {
let api_url =`${objID}/records`
let options ={
method: 'GET',
headers: headers

if(typeof filter !=='undefined'){
api_url += '?filters=' + encodeURIComponent(JSON.stringify(filter)) + '&sort_field=' + sortObj.field + '&sort_order=' + sortObj.order
api_url += '/' + recordID
let response = fetch(api_url, options);
let data =JSON.parse(response.getContextText())
return data