Need to access data in JSON.stringify object

问题

The background for this question is I'm trying to access the selected cell from addListener in google visualization calendar. I could print the selected cell using JSON.stringify(chart.getSelection());. It prints as [{"date":1468195200000,"row":0}].

My problem is to access this date object. I tried to access it as

var obj=JSON.stringify(chart.getSelection());
        console.log('selected value '+obj.date);

But it displays as Undefined. When I print the obj it displays as [object, object]

If you need more information please let me know. Any suggestion would be appreciated.

回答1:

JSON.stringify() serializes a data object into a string. Just access the object directly.

var data = chart.getSelection()[0]; // assuming there is only ever one item in the selection array.
console.log(data.date)

回答2:

Try this:

var data = [{"date":1468195200000,"row":0}]

var rw = data[0].row;
var dt = new Date(data[0].date);

console.log(rw);
console.log(dt);

回答3:

careful when accessing the first array element directly when listening for the 'select' event

chart.getSelection()[0]

the 'select' event is fired, both when a selection is made, AND removed

so the above line will fail when the selection is removed

check the length before accessing...

  selection = chart.getSelection();
  // check selection length
  if (selection.length > 0) {
    console.log(selection[0].date);
  } else {
    console.log('selection removed');
  }

see following working snippet, select a date, then select again to remove the selection...

google.charts.load('current', {
  callback: function () {
    var dataTable = new google.visualization.DataTable();
    dataTable.addColumn({ type: 'date', id: 'Date' });
    dataTable.addColumn({ type: 'number', id :'Score' });
    dataTable.addRows([
      [ new Date(2016, 3, 13), 101 ],
      [ new Date(2016, 3, 14), 102 ],
      [ new Date(2016, 3, 15), 103 ],
      [ new Date(2016, 3, 16), 104 ],
      [ new Date(2016, 3, 17), 105 ]
    ]);

    var chart = new google.visualization.Calendar(document.getElementById('chart_div'));
    google.visualization.events.addListener(chart, 'select', function () {
      var selection = chart.getSelection();

      // check selection length
      if (selection.length > 0) {
        console.log(selection[0].date);
      } else {
        console.log('selection removed');
      }
    });
    chart.draw(dataTable);
  },
  packages:["calendar"]
});

<script src="https://www.gstatic.com/charts/loader.js"></script>
<div id="chart_div"></div>

回答4:

This is an array of objects however there is only one object in this array (or so I think) so what you should do is console.log(obj[0].date); instead!

来源：https://stackoverflow.com/questions/38319107/need-to-access-data-in-json-stringify-object