Object.assign({ style: ‘expanded’ }, options); ????

Seems like you are missing an assignment such as:

let newOptions = Object.assign({ style: ‘expanded’ }, options);

or even:

options = Object.assign({ style: ‘expanded’ }, options);

Other than that, I fully enjoyed reading your article as I have given up using Gulp/Grunt for about a year now and haven’t really missed either.