Q: Embed API Third party visualization > Uncaught TypeError: Cannot set property 'innerHTML' of null (cb=gapi.loaded_0:139) First of all, I would like to apologize about my poor web programming skill. I'm still new to Javascript.
Here is my problem : I get an Uncaught TypeError while trying to reproduce the  [Embed Api guide for Google Analytics]
The exact error I get : Uncaught TypeError: Cannot set property 'innerHTML' of null (cb=gapi.loaded_0:139)
I looked for an answer but didn't find any that was working.
Here is my full code :
<head>
<script>
(function(w,d,s,g,js,fs){
  g=w.gapi||(w.gapi={});g.analytics={q:[],ready:function(f){this.q.push(f);}};
  js=d.createElement(s);fs=d.getElementsByTagName(s)[0];
  js.src='https://apis.google.com/js/platform.js';
  fs.parentNode.insertBefore(js,fs);js.onload=function(){g.load('analytics');};
}(window,document,'script'));
</script>
<script src="https://ga-dev-tools.appspot.com/public/javascript/Chart.min.js"></script>
<script src="https://ga-dev-tools.appspot.com/public/javascript/moment.min.js"></script>
<script src="https://ga-dev-tools.appspot.com/public/javascript/embed-api/components/view-selector2.js"></script>
<script src="https://ga-dev-tools.appspot.com/public/javascript/embed-api/components/date-range-selector.js"></script>
<script src="https://ga-dev-tools.appspot.com/public/javascript/embed-api/components/active-users.js"></script>    
</head>
<body>
<div id="embed-api-auth-container"></div>
<div id="view-selector-container"></div>
<div id="active-users-container"></div>
<div id="chart-1-container"></div>
<div id="legend-1-container"></div>
<div id="chart-2-container"></div>
<div id="legend-2-container"></div>
<div id="chart-3-container"></div>
<div id="legend-3-container"></div>
<div id="chart-4-container"></div>
<div id="legend-4-container"></div>
</body>
<script>
window.onload = function()
{
gapi.analytics.ready(function() {

  gapi.analytics.auth.authorize({
    container: 'embed-api-auth-container',
    clientid: 'xxxxxxxxxx.apps.googleusercontent.com',
  });

  var activeUsers = new gapi.analytics.ext.ActiveUsers({
    container: 'active-users-container',
    pollingInterval: 5
  });

  activeUsers.once('success', function() {
    var element = this.container.firstChild;
    var timeout;

    this.on('change', function(data) {
      var element = this.container.firstChild;
      var animationClass = data.delta > 0 ? 'is-increasing' : 'is-decreasing';
      element.className += (' ' + animationClass);

      clearTimeout(timeout);
      timeout = setTimeout(function() {
        element.className =
            element.className.replace(/ is-(increasing|decreasing)/g, '');
      }, 3000);
    });
  });

  var viewSelector = new gapi.analytics.ext.ViewSelector2({
    container: 'view-selector-container',
  })
  .execute();

  viewSelector.on('viewChange', function(data) {
    var title = document.getElementById('view-name');
    title.innerHTML = data.property.name + ' (' + data.view.name + ')';

    activeUsers.set(data).execute();

    renderWeekOverWeekChart(data.ids);
    renderYearOverYearChart(data.ids);
    renderTopBrowsersChart(data.ids);
    renderTopCountriesChart(data.ids);
  });

  function renderWeekOverWeekChart(ids) {

    var now = moment(); // .subtract(3, 'day');

    var thisWeek = query({
      'ids': ids,
      'dimensions': 'ga:date,ga:nthDay',
      'metrics': 'ga:sessions',
      'start-date': moment(now).subtract(1, 'day').day(0).format('YYYY-MM-DD'),
      'end-date': moment(now).format('YYYY-MM-DD')
    });

    var lastWeek = query({
      'ids': ids,
      'dimensions': 'ga:date,ga:nthDay',
      'metrics': 'ga:sessions',
      'start-date': moment(now).subtract(1, 'day').day(0).subtract(1, 'week')
          .format('YYYY-MM-DD'),
      'end-date': moment(now).subtract(1, 'day').day(6).subtract(1, 'week')
          .format('YYYY-MM-DD')
    });

    Promise.all([thisWeek, lastWeek]).then(function(results) {

      var data1 = results[0].rows.map(function(row) { return +row[2]; });
      var data2 = results[1].rows.map(function(row) { return +row[2]; });
      var labels = results[1].rows.map(function(row) { return +row[0]; });

      labels = labels.map(function(label) {
        return moment(label, 'YYYYMMDD').format('ddd');
      });

      var data = {
        labels : labels,
        datasets : [
          {
            label: 'Last Week',
            fillColor : "rgba(220,220,220,0.5)",
            strokeColor : "rgba(220,220,220,1)",
            pointColor : "rgba(220,220,220,1)",
            pointStrokeColor : "#fff",
            data : data2
          },
          {
            label: 'This Week',
            fillColor : "rgba(151,187,205,0.5)",
            strokeColor : "rgba(151,187,205,1)",
            pointColor : "rgba(151,187,205,1)",
            pointStrokeColor : "#fff",
            data : data1
          }
        ]
      };

      new Chart(makeCanvas('chart-1-container')).Line(data);
      generateLegend('legend-1-container', data.datasets);
    });
  }
  function renderYearOverYearChart(ids) {

    var now = moment(); // .subtract(3, 'day');

    var thisYear = query({
      'ids': ids,
      'dimensions': 'ga:month,ga:nthMonth',
      'metrics': 'ga:users',
      'start-date': moment(now).date(1).month(0).format('YYYY-MM-DD'),
      'end-date': moment(now).format('YYYY-MM-DD')
    });

    var lastYear = query({
      'ids': ids,
      'dimensions': 'ga:month,ga:nthMonth',
      'metrics': 'ga:users',
      'start-date': moment(now).subtract(1, 'year').date(1).month(0)
          .format('YYYY-MM-DD'),
      'end-date': moment(now).date(1).month(0).subtract(1, 'day')
          .format('YYYY-MM-DD')
    });

    Promise.all([thisYear, lastYear]).then(function(results) {
      var data1 = results[0].rows.map(function(row) { return +row[2]; });
      var data2 = results[1].rows.map(function(row) { return +row[2]; });
      var labels = ['Jan','Feb','Mar','Apr','May','Jun',
                    'Jul','Aug','Sep','Oct','Nov','Dec'];

      for (var i = 0, len = labels.length; i < len; i++) {
        if (data1[i] === undefined) data1[i] = null;
        if (data2[i] === undefined) data2[i] = null;
      }

      var data = {
        labels : labels,
        datasets : [
          {
            label: 'Last Year',
            fillColor : "rgba(220,220,220,0.5)",
            strokeColor : "rgba(220,220,220,1)",
            data : data2
          },
          {
            label: 'This Year',
            fillColor : "rgba(151,187,205,0.5)",
            strokeColor : "rgba(151,187,205,1)",
            data : data1
          }
        ]
      };

      new Chart(makeCanvas('chart-2-container')).Bar(data);
      generateLegend('legend-2-container', data.datasets);
    })
    .catch(function(err) {
      console.error(err.stack);
    })
  }

  function renderTopBrowsersChart(ids) {

    query({
      'ids': ids,
      'dimensions': 'ga:browser',
      'metrics': 'ga:pageviews',
      'sort': '-ga:pageviews',
      'max-results': 5
    })
    .then(function(response) {

      var data = [];
      var colors = ['#4D5360','#949FB1','#D4CCC5','#E2EAE9','#F7464A'];

      response.rows.forEach(function(row, i) {
        data.push({ value: +row[1], color: colors[i], label: row[0] });
      });

      new Chart(makeCanvas('chart-3-container')).Doughnut(data);
      generateLegend('legend-3-container', data);
    });
  }


  function renderTopCountriesChart(ids) {
    query({
      'ids': ids,
      'dimensions': 'ga:country',
      'metrics': 'ga:sessions',
      'sort': '-ga:sessions',
      'max-results': 5
    })
    .then(function(response) {

      var data = [];
      var colors = ['#4D5360','#949FB1','#D4CCC5','#E2EAE9','#F7464A'];

      response.rows.forEach(function(row, i) {
        data.push({
          label: row[0],
          value: +row[1],
          color: colors[i]
        });
      });

      new Chart(makeCanvas('chart-4-container')).Doughnut(data);
      generateLegend('legend-4-container', data);
    });
  }



  function query(params) {
    return new Promise(function(resolve, reject) {
      var data = new gapi.analytics.report.Data({query: params});
      data.once('success', function(response) { resolve(response); })
          .once('error', function(response) { reject(response); })
          .execute();
    });
  }



  function makeCanvas(id) {
    var container = document.getElementById(id);
    var canvas = document.createElement('canvas');
    var ctx = canvas.getContext('2d');

    container.innerHTML = 'chart-3-container';
    canvas.width = container.offsetWidth;
    canvas.height = container.offsetHeight;
    container.appendChild(canvas);

    return ctx;
  }



  function generateLegend(id, items) {
    var legend = document.getElementById(id);
    legend.innerHTML = items.map(function(item) {
      var color = item.color || item.fillColor;
      var label = item.label;
      return '<li><i style="background:' + color + '"></i>' + label + '</li>';
    }).join('');
  }


  Chart.defaults.global.animationSteps = 60;
  Chart.defaults.global.animationEasing = 'easeInOutQuart';
  Chart.defaults.global.responsive = true;
  Chart.defaults.global.maintainAspectRatio = false;

})};
</script>
</html>

I'm sorry about this question, I'm sure the answer is pretty dumb... Thank you for taking some time to help me.

A: There are possibly more cases of this error in that block of code but this is the first one I came across:
var title = document.getElementById('view-name');
    title.innerHTML = data.property.name + ' (' + data.view.name + ')';
This will cause the "Cannot set property 'innerHTML' of null" error because you don't have an element on the page with the id of 'view-name', therefore title = null when you are calling innerHTML on it. 
