code: function localExport(opt) {
      var ind = _.reGet(/\d/)(opt.chart.renderTo);
      _.assign(opt, {
        'exporting': {
          'buttons': {
            'contextButton': {
              'y': -10,
              'menuItems': [{
                'text': 'Save as PNG',
                onclick: function() {
                  this.createCanvas(opt.title, 'png', ind);
                },
                'separator': false
              }, {
                'text': 'Save as JPEG',
                onclick: function() {
                  this.createCanvas(opt.title, 'jpeg', ind);
                },
                'separator': false
              }]
            }
          }
        }
      })
      return opt;
    }
docs: extending exporting properties for local save