角4 ckeditor-未捕获的TypeError：无法读取未定义的属性'getSelection'

Question

我正在为我的angular 4应用程序实现ckeditor。 一切工作正常，但是当我使用浏览器后退按钮从另一个页面返回时，编辑器挂起，出现以下错误

ckeditor.js:445 Uncaught TypeError: Cannot read property 'getSelection' of undefined
at CKEDITOR.dom.selection.getNative (ckeditor.js:445)
at CKEDITOR.dom.selection (ckeditor.js:443)
at a.CKEDITOR.editor.getSelection (ckeditor.js:440)
at CKEDITOR.plugins.undo.Image (ckeditor.js:1072)
at CKEDITOR.plugins.undo.UndoManager.save (ckeditor.js:1067)
at a.<anonymous> (ckeditor.js:1063)
at a.n (ckeditor.js:10)
at a.CKEDITOR.event.CKEDITOR.event.fire (ckeditor.js:12)
at a.CKEDITOR.editor.CKEDITOR.editor.fire (ckeditor.js:13)
at CKEDITOR.command.exec (ckeditor.js:952)

当我深入研究代码时，我发现错误在于下面的函数中，其中this.document.getWindow().$是未定义的，它尝试在该函数上调用函数。

        getNative: function() {
            return void 0 !== this._.cache.nativeSel ? this._.cache.nativeSel : this._.cache.nativeSel = x ? this.document.$.selection : this.document.getWindow().$.getSelection()
        }