问为什么我在挂载钩子时出现错误："TypeError: E is undefined"？

EN

methods: {
    pushFolders: function() {
      $.each(this.$store.state.folders.subFolders, function(key, value) {

        this.selected.push(value.uuid)

      }.bind(this));
    },
    checkAll: function(){

      this.isSelectedAll = !this.isSelectedAll;
      this.selectedFolders = [];
      if(this.isSelectedAll){ // Check all
        // this.selectedFolders.push(this.selected[key]);
        this.$store.dispatch('SELECT_FOLDERS',this.selected)
      }
    }
  },
  mounted: function() {
    this.pushFolders()
  }

Error in mounted hook: "TypeError: e is undefined"