What do you look for in programming ebooks?

The best way I've seen books laid out is having all the core concepts in a section, and in each section have example code on the right and on the left the explanation of the code along with a little bit of context and theory, for more in-depth theory, condense it, make writing style simple for a Jr. dev to understand, but short theory and code samples (good ones, not using cars and fruit as examples, make it business oriented since most devs work for businesses). It's hard to find these books, but when I do, I get them, also a great publisher that does this is Murach books, you should check out their format and copy it, problem is they only have a few areas they cover.

My definition of perfection can be summarized as simple, concise and valuable.

React's documentation is a fantastic example. It's simple enough for a junior dev to understand (not many fancy terms, great pace of progression). But it also provides enough value and conciseness, which is appreciated by more experienced programmers.

Compare to Angular's , which is full of programming lingo and obscure "explanations" that impress no-one and make it overly difficult to figure out what they hell they're trying to explain.

To be honest for niche books I think theory is far more important than code as you could find plenty of it on web.
Say JavaScript, one can find loads of online tutorials/code on web for specefic tasks however a descent theory on prototypes or other core concepts are difficult to come by.
Again my preference depends a lot on the topic, but I generally tend to like books having loads of theory (also keeps me from being tempted to read code and skip over).