Ckeditor onchange - why does my code work 2 times?

Question

JavaScript

Hello. Setting up ckeditor. Downloaded the onchange plugin ( https://ckeditor.com/cke4/addon/onchange). Connected it in config.js:
config.extraPlugins = 'onchange';
Wrote the following code in config.js:

CKEDITOR.on('instanceReady', function (ev) {
    var editor = ev.editor;
    editor.on('change', function() {
        console.log('zzz');
    });
});

And now when I write something in my editor, zzz is displayed twice. Why is that? Should be output only once.