Changing value of global javascript variable

Question

I'm attempting to change the value of a global variable inside a javascript function, however, the value does not seem to be taken, and I'm not sure why. (Admittedly, I am not an experienced javascript person.) Here is my code:

var title_chart = "";

google.load("visualization", "1", {packages:["corechart"]});

google.setOnLoadCallback(drawChart);

function drawChart() {
  var data = new google.visualization.DataTable();
  data.addColumn('string', 'Country');
  data.addColumn('number', 'Number of Entries');

  jQuery.getJSON('/data/stats.json', function(chart_data) {
    title_chart = chart_data.chart_title;
    jQuery.each(chart_data.stats, function(index, value){
      data.addRows(1);
      data.setValue(index, 0, value.chart_label);
    });
  });

  var chart = new google.visualization.PieChart(document.getElementById('chart_div'));
  chart.draw(data, {width: 450, height: 300, title: title_chart});

}

Thanks!

You need to use window.variable="value you want to set" to set the value of global javascript variable see the link for you reference javatpoint.com/oprweb/test.jsp?filename=jsglobalvariable2 — showmyroutes
– showmyroutes, Commented Jun 1, 2017 at 5:45

Matthew Flaschen · Accepted Answer · 2010-07-22 05:38:37Z

1

getJSON is asynchronous. Do this instead:

jQuery.getJSON('/data/stats.json', function(chart_data) {
  var title_chart = chart_data.chart_title;
  jQuery.each(chart_data.stats, function(index, value){
    data.addRows(1);
    data.setValue(index, 0, value.chart_label);
  });

  var chart = new google.visualization.PieChart(document.getElementById('chart_div'));
  chart.draw(data, {width: 450, height: 300, title: title_chart});
});

The issue is that getJSON returns immediately. Only later, when the request completes, is your callback called. In the meantime, chart.draw may have already run. By moving this code into the callback function, we ensure it runs at the right time. Also note that we can eliminate the global.

answered Jul 22, 2010 at 5:38

Matthew Flaschen

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