discourse/app/assets/javascripts/admin/controllers/admin_reports_controller.js

Discourse.AdminReportsController = Ember.ObjectController.extend({
  viewMode: 'table',

  viewingTable: Em.computed.equal('viewMode', 'table'),
  viewingBarChart: Em.computed.equal('viewMode', 'barChart'),

  // Changes the current view mode to 'table'
  viewAsTable: function() {
    this.set('viewMode', 'table');
  },

  // Changes the current view mode to 'barChart'
  viewAsBarChart: function() {
    this.set('viewMode', 'barChart');
  }

});