ES6 exports/imports use-case, compared to traditional namespacing

Question

I don't understand WHY and in what scenario this would be used..

My current web setup consists of lots of components, which are just functions or factory functions, each in their own file, and each function "rides" the app namespace, like : app.component.breadcrumbs = function(){... and so on.

Then GULP just combines all the files, and I end up with a single file, so a page controller (each "page" has a controller which loads the components the page needs) can just load it's components, like: app.component.breadcrumbs(data).

All the components can be easily accessed on demand, and the single javascript file is well cached and everything. This way of work seems extremely good, never saw any problem with this way of work. of course, this can (and is) be scaled nicely.

So how are ES6 imports for functions any better than what I described?

what's the deal with importing functions instead of just attaching them to the App's namespace? it makes much more sense for them to be "attached".

Files structure

/dist/app.js                     // web app namespace and so on
/dist/components/breadcrumbs.js  // some component
/dist/components/header.js       // some component
/dist/components/sidemenu.js     // some component
/dist/pages/homepage.js          // home page controller

// GULP concat all above to
/js/app.js // this file is what is downloaded

Then inside homepage.js it can look like this:

app.routes.homepage = function(){
    "use strict";
    var DOM = { page : $('#page') };

    // append whatever components I want to this page
    DOM.page.append(
        app.component.header(),
        app.component.sidemenu(),
        app.component.breadcrumbs({a:1, b:2, c:3})
    )
};

This is an extremely simplified code example but you get the point

Answer 1

Answers to this are probably a little subjective, but I'm going to do my best.

At the end of the day, both methods allow support creating a namespace for a piece of functionality so that it does not conflict with other things. Both work, but in my view, modules, ES6 or any other, provide a few extra benefits.

Explicit dependencies

Your example seems very bias toward a "load everything" approach, but you'll generally find that to be uncommon. If your components/header.js needs to use components/breadcrumbs.js, assumptions must be made. Has that file been bundled into the overall JS file? You have no way of knowing. You're two options are

1. Load everything
2. Maintain a file somewhere that explicitly lists what needs to be loaded.

The first option is easy and in the short term is probably fine. The second is complicated for maintainability because it would be maintained as an external list, it would be very easy to stop needing one of your component file but forget to remove it.

It also means that you are essentially defining your own syntax for dependencies when again, one has now been defined in the language/community.

What happens when you want to start splitting your application into pieces? Say you have an application that is a single large file that drives 5 pages on your site, because they started out simple and it wasn't big enough to matter. Now the application has grown and should be served with a separate JS file per-page. You have now lost the ability to use option #1, and some poor soul would need to build this new list of dependencies for each end file.

What if you start using a file in a new places? How do you know which JS target files actually need it? What if you have twenty target files?

What if you have a library of components that are used across your whole company, and one of they starts relying on something new? How would that information be propagated to any number of the developers using these?

Modules allow you to know with 100% certainty what is used where, with automated tooling. You only need to package the files you actually use.

Ordering

Related to dependency listing is dependency ordering. If your library needs to create a special subclass of your header.js component, you are no longer only accessing app.component.header() from app.routes.homepage(), which would presumable be running at DOMContentLoaded. Instead you need to access it during the initial application execution. Simple concatenation offers no guarantees that it will have run yet. If you are concatenating alphabetically and your new things is app.component.blueHeader() then it would fail.

This applies to anything that you might want to do immediately at execution time. If you have a module that immediately looks at the page when it runs, or sends an AJAX request or anything, what if it depends on some library to do that?

This is another argument agains #1 (Load everything) so you start having to maintain a list again. That list is again going to be a custom things you'll have come up with instead of a standardized system.

How do you train new employees to use all of this custom stuff you've built?

Modules execute files in order based on their dependencies, so you know for sure that the stuff you depend on will have executed and will be available.

Scoping

Your solution treats everything as a standard script file. That's fine, but it means that you need to be extremely careful to not accidentally create global variables by placing them in the top-level scope of a file. This can be solved by manually adding (function(){ ... })(); around file content, but again, it's one more things you need to know to do instead of having it provided for you by the language.

Conflicts

app.component.* is something you've chosen, but there is nothing special about it, and it is global. What if you wanted to pull in a new library from Github for instance, and it also used that same name? Do you refactor your whole application to avoid conflicts?

What if you need to load two versions of a library? That has obvious downsides if it's big, but there are plenty of cases where you'll still want to trade big for non-functional. If you rely on a global object, it is now up to that library to make sure it also exposes an API like jQuery's noConflict. What if it doesn't? Do you have to add it yourself?

Encouraging smaller modules

This one may be more debatable, but I've certainly observed it within my own codebase. With modules, and the lack of boilerplate necessary to write modular code with them, developers are encouraged to look closely on how things get grouped. It is very easy to end up making "utils" files that are giant bags of functions thousands of lines long because it is easier to add to an existing file that it is to make a new one.

Dependency webs

Having explicit imports and exports makes it very clear what depends on what, which is great, but the side-effect of that is that it is much easier to think critically about dependencies. If you have a giant file with 100 helper functions, that means that if any one of those helpers needs to depend on something from another file, it needs to be loaded, even if nothing is ever using that helper function at the moment. This can easily lead to a large web of unclear dependencies, and being aware of dependencies is a huge step toward thwarting that.

Standardization

There is a lot to be said for standardization. The JavaScript community has moved heavily in the direction of reusable modules. This means that if you hope into a new codebase, you don't need to start off by figuring out how things relate to eachother. Your first step, at least in the long run, won't be to wonder whether something is AMD, CommonJS, System.register or what. By having a syntax in the language, it's one less decision to have to make.

The long and short of it is, modules offer a standard way for code to interoperate, whether that be your own code, or third-party code.

Your current process is to concatenate everything always into a single large file, only ever execute things after the whole file has loaded and you have 100% control over all code that you are executing, then you've essentially defined your own module specification based on your own assumptions about your specific codebase. That is totally fine, and no-one is forcing you to change that.

No such assumptions can be made for the general case of JavaScript code however. It is precisely the objective of modules to provide a standard in such a way as to not break existing code, but to also provide the community with a way forward. What modules offer is another approach to that, which is one that is standardized, and one that offers clearer paths for interoperability between your own code and third-party code.