I saw this "then-heavy" style in many places, but I never really understood: I find perfectly fine to make "fadeIn" return a promise, or an ajax call, and find "the right way" to join them with then / when / Promise.all etc.

But what is the meaning to add a lambda function as "response => response.json()" in a then? why a different lambda "json => el.innerHTML = json.results[2].message" ?

isn't it a "gratuitous" use of a then-able object? I found more readable to have a (sincronous, debuggable, "old-style") function without the need to split in one thousand one line lambdas.

moreover, my python background makes me looks as "ugly" the last one, as it's a lambda function with an assignement, and not a simple expression.