Why most of developer uses libraries and frameworks but they didn't try to read it's source to learn from it ?

Basm allah alrahman alrahim

like Abdelbasset Benguelloula and like others friends said (fast forious)

I think because there are not expert but junior.

I don't understand how a web developer can develop without read source javascript.

I'm always confronted with debug my code inside vendor libraries on Chrome developer tools.

This practice is very helpful to figure out the behavior of vendor sources, and to learn it by the same way.

Thank you for the question, simply because you get the job done in less time with less effort...it is the least action principle which govern our world :)

Most developers are fluent in programming languages when used in real projects, so They do not have time to read more about it.

A framework is not absolutely necessary: it is “just” one of the tools that is available to help you develop better and faster!Better, because a framework provides you with the certainty that you are developing an application that is in full compliance with the business rules, that is structured, and that is both maintainable and upgradable.Faster, because it allows developers to save time by re-using generic modules in order to focus on other areas. Without, however, ever being tied to the framework itself.

It is very easy for the developer to use the libraries. But the project estimated time doesn't permit the developer to learn its source.

Begaine from other ended

Thats is speedly and less hardly from writing full code 

And librares is important tool for object orinted

If I had enough time, I would  read it