fetchdata.js

// window.onload = getJSON;
function setQuery() {
  // to process the url to be sent to the server
  const site = 'http://gymk-back.herokuapp.com' + events;
  let temp = site.split('/');
  let final = 'http://gymk-back.herokuapp.com/' + temp[temp.length - 1];
  return final;
}

async function getJSON() {
  let policy = {
    mode: 'no-cors'
  };

  fetch('http://gymk-back.herokuapp.com/events', policy)
    .then(function(response) {
      // url in place of link later
      console.log(response);
    })
    .then(function(data) {
      console.log(data); // constructTable(data);
    })
    .catch(function(error) {
      console.log(error);
    });
}
getJSON();

function constructTable() {
  var data = JSON.stringify('json file here'); //JSON.stringify('json file here');

  /* sample format of JSON file [
                {
                    "Book ID": "1",
                    "Book Name": "Computer Architecture",
                    "Category": "Computers",
                    "Price": "125.60"
                },
                {
                    "Book ID": "2",
                    "Book Name": "Asp.Net 4 Blue Book",
                    "Category": "Programming",
                    "Price": "56.00"
                },
                {
                    "Book ID": "3",
                    "Book Name": "Popular Science",
                    "Category": "Science",
                    "Price": "210.40"
                }
            ] */ var heads = [];

  for (let i = 0; i < data.length; i++) {
    // get headings
    for (var key in data[i]) {
      if (heads.indexOf(key) === -1) {
        heads.push(key);
      }
    }
  }
  var table = document.getElementById('event'); // change id accordingly

  var tr = table.insertRow(-1);

  for (let i = 0; i < heads.length; i++) {
    var th = document.createElement('th');
    th.innerHTML = heads[i];
    tr.appendChild(th);
  }

  for (let i = 0; i < data.length; i++) {
    tr = table.insertRow(-1);
    for (let j = 0; j < heads.length; j++) {
      var tabcell = tr.insertCell(-1);
      tabcell.innerHTML = data[i][heads[j]];
    }
  }
}

/*
function getJSON() {
let policy = {
    mode: 'no-cors'
}
const response = await fetch('http://gymk-back.herokuapp.com/events', policy);
const myJson = await response.json();

fetch('http://gymk-back.herokuapp.com/events', policy).then(function (response) {
    return response.json();
}).then(function (data) {
    console.log(data);   // constructTable(data);
}).catch(function (error) {
    console.log(error);
});
}

function getQuery(url) {
    const response = await fetch(url);
    const result = await response.json();
    // console.log(JSON.stringify(myJson));
    return result;
}

var getJSON = function(url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.responseType = 'json';
    xhr.onload = function() {
        var status = xhr.status;
        if (status === 200) {
            callback(null, xhr.response);
        } else {
            callback(status, xhr.response);
        }
    };
    xhr.send();
};

getJSON(setQuery(),
    function(err, data) {
        if (err !== null) {
            alert('Something went wrong: ' + err);
        } else {
            alert('Your query count: ' + data.query.count);
        }
}); */