如何在angular JS应用程序中实现分层X轴条形图。工具栏应该有+/-来打开/关闭分层数据，如下所示

<div ng-controller="BarChartController">
  <button ng-click="toggleLayer()">+/-</button>
  <div ng-repeat="data in chartData" ng-style="{'width': data.width, 'background-color': data.color}">
    {{data.label}}
  </div>
</div>

angular.module('myApp', [])
  .controller('BarChartController', function($scope) {
    $scope.chartData = [
      {label: 'Layer 1', width: '100px', color: 'red'},
      {label: 'Layer 2', width: '80px', color: 'blue'},
      {label: 'Layer 3', width: '60px', color: 'green'}
    ];
    
    $scope.showLayer = false;
    
    $scope.toggleLayer = function() {
      $scope.showLayer = !$scope.showLayer;
    };
  });