How to use the @jupyter-widgets/controls.BoxView function in @jupyter-widgets/controls

return {
            ...super.defaults(),
            _model_name: "ExatomicBoxModel",
            _view_name: "ExatomicBoxView",
            _model_module_version: semver,
            _view_module_version: semver,
            _model_module: "exatomic",
            _view_module: "exatomic",
            linked: false
        }
    }

}


export class ExatomicBoxView extends control.BoxView {

    initialize(parameters) {
        super.initialize(parameters)
        this.init()
    }

    init() {
        this.init_listeners()
        var that = this
        this.displayed.then(function() {
            that.scene_ps = that.children_views.views[1].then(function(vbox) {
                var hboxs = vbox.children_views.views
                var promises = Promise.all(hboxs).then(function(hbox) {
                    var subpromises = []
                    for (var i = 0; i < hbox.length; i++) {
                        var scns = hbox[i].children_views.views