用自定义库包装jQuery，dojo？

Question

Coming from Java, I'm wondering if a Java best practice applies to JavaScript.

In Java, there's a separation of interface and implementation, and mixing them up is considered a bad practice. By the same token, it is recommended to hide implementation details of your library from end developers.

For example, log4J is one of the most popular logging libraries out there but it is recommended to write code to the slf4j library or the Commons Logging library that "wraps" log4j. This way, if you choose to switch to another logging framework such as logback, you can do so without changing your code. Another reason is that you, as a user of a logging library, how logging is done is none of your concern, as long as you know what logging does.

So back to JavaScript, most non-trivial web applications have their own custom JavaScript libraries, many of which use open source libraries such as jQuery and dojo. If a custom library depends on, say jQuery, not as an extension, but as implementation, do you see the need to add another layer that wraps jQuery and makes it transparent to the rest of JavaScript code?

For example, if you have the foo library that contains all your custom, front-end logic, you'd introduce the bar library that just wraps jQuery. This way, your foo library would use the bar library for jQuery functions, but it is totally oblivious to jQuery. In theory, you could switch to other libraries such as dojo and google web toolkit without having a big impact on the foo library.

Do you see any practical value in this? Overkill?

Answer 1

Although it makes sense from a theoretical standpoint, in practice I'd say it's overkill. If nothing else for these two reasons:

1. Anything that adds to the size of the request (or adds more requests) is bad - in web world, less is more.
2. If you're using say jQuery, the chances of you switching to something like Mootools is (imho) slim to none. From what I've seen, the top libraries each aim to solve different problems (at least in the case of Mootools and jQuery - see this great doc for more info on that). I'd assume that you'd incur a tremendous amount of headache if you were to try to implement a middleware library that could easily switch between the two.

Answer 2

In my experience and being a Java developer myself, sometimes we tend to take the whole "abstraction" layer pattern too far, I've seen implementations where someone decided to completely abstract a certain framework just for the sake of "flexibility" but it ends up making things more complicated and creating more code to maintain.

Bottom line is you should look at it on a case by case basis, for example you wouldn't try to create an abstraction layer on top of struts, or on top of JPA, just in case you then go to a different framework (which I've rarely seen done).

My suggestion is, regardless of the framework you are using, create objects and components that use the framework internally, they should model your problem and be able to interact between them without the need of any specific framework.

Hope this helps.

Answer 3

There are a lot of good answers here, but one thing I don't see mentioned is feature sets. If you try to write a library to wrap the functionality provided by, say, jQuery, but you want to be able to easily swap out for something like prototype, you have a problem. The jQuery library doesn't provide all the features prototype provides, and prototype doesn't provide all the features jQuery provides. On top of that, they both provide their features in radically different ways (prototype extends base objects -- that's damn near impossible to wrap).

In the end, if you tried to wrap these libraries in some code that adds 'abstraction' to try to make them more flexible, you're going to lose 80% of what the frameworks provided. You'll lose the fancy interfaces they provide (jQuery provides an awesome $('selector') function, prototype extends base objects), and you'll also have to decide if you want to leave out features. If a given feature is not provided by both frameworks, you have to either ditch it or reimplement it for the other framework. This is a big can of worms.

The whole problem stems from the fact that Java is a very inflexible language. A library provides functionality, and that's it. In JavaScript, the language itself is insanely flexible, and lets you do lots of crazy things (like writing a library, and assigning it to the $ variable). The ability to do crazy things lets developers of javascript libraries provide some really creative functionality, but it means you can't just find commonalities in libraries and write an abstraction. I think writing javascript well requires a significant change in perspective for a Java developer.

Answer 4

Someone wise once said "premature optimization is the root of all evil." I believe that applies in this case.

As others have expressed, you don't want to abstract for the sake of flexibility until you have an actual need for the abstraction. Otherwise you end up doing more work than necessary, and introducing unnecessary complexity before it is required. This costs money and actually makes your code more brittle.

Also, if your code is well organized and well tested, you should not be afraid of major changes. Code is always changing, and trying to anticipate and optimize for a change that may or may not come will almost always get you in more trouble than it saves you.

Acknowledgement: I should give credit to Agile programming and my practice and readings on the topic. What I've said comes directly from my understanding of Agile, and I've found it to be an extremely good razor to cut out the extra fat of my work and get lots done. Also none of what I've said is actually JavaScript specific... I'd apply those principles in any language.

Answer 5

There are good arguments calling this development practice - wrapping in order to switch later - into question in any language.

A good quote by Oren Eini, from his writeup on wrapping ORMs :

Trying to encapsulate to make things easier to work with, great. Trying to encapsulate so that you can switch OR/Ms? Won't work, will be costly and painful.

Answer 6

This is definitely something that is done in enterprise environments.

Take for example a company that has their own custom javascript framework that is used on all of their projects. Each of the projects decide to use their own framework (jQuery, Dojo, Prototype) to add functionality to the underlying modules of the company framework. Employees that move between projects can now easily do so because their API with working the project's codebase is still the same, even though the underlying implementation could be different for each project. Abstraction is helpful in these situations.

Answer 7

It is overkill. Javascript is not Java and is not in any way related to Java. It is a completely different language that got Java in the name for marketing reasons.

If you are concerned with availability of add-on libraries, then choose a framework with a large ecosystem. In an enterprise environment you will be further ahead by standardising on a vanilla off-the-shelf uncustomised web framework that you can upgrade every year or so tracking the rest of the world. And then supplement that with a SMALL in-house add-on library which you will, of course, have to maintain yourself, not to mention training any new programmers that you hire.

Since you are talking about Javascript in the client (web browser) it is more important that you limit the complexity of the things that people do with it. Don't build huge amounts of client side code, and don't make stuff that is so brittle that another programmer can't maintain it. A web framework helps you both keep the linecount down, and keep your own code reasonably simple.

It is not a question of Javascript best practice, because that would be different for server-side JS such as Rhino or node.js.

Answer 8

Adapter pattern is not a common solution in this case. The only example I know to use this pattern is extjs . Javascript projects are usually too small and they aren't worth the effort you would make by creating such an abstraction layer. The common solution for this problem is that you try to use multiple frameworks together for example with jquery.noConflict .

Answer 9

I've done this before, and can talk a bit about the experience of writing a library/toolkit wrapper.

The plan was to move from Prototype to some other library. Dojo was the first choice, but at the time I wasn't sure whether that's the library to move everything to (and by everything I mean ~5MB of Prototype-happy JS). So coming from a world of clean interfaces, I was set to write one around Prototype and Dojo; an awesome interface that would make switching out from dojo a breeze, if that was in fact necessary.

That was a mistake that cost a lot of time and effort for a few reasons. The first one is that although two libraries can provide the same functionality, (a) their API will almost always be different, and most importantly (b) the way you program with one library will be different.

To demonstrate, let's take something as common as adding a class-name:

// Prototype
$("target").addClassName('highlighted');

// Dojo
dojo.addClass("target", "highlighted");

// jQuery
$("target").addClass("highlighted");

// MooTools
$('target').set('class', 'highlighted');

Pretty straight-forward so far. Let's complicate it a bit:

// Prototype
Element.addClassName('target', 'highlighted selected');

// Dojo
dojo.addClass("target", ["highlighted", "selected"]);

// jQuery
$("target").addClass(function() {
   return 'highlighted selected';
});

// MooTools
$("target").set({
    "class": "highlighted selected"
});

Now after choosing an interface for your version of the addClass you have two options: (1) code to the lowest common denominator, or (2) implement all of the non-intersecting features of the libraries.

If you go with the 1st -- you'll loose the "personality" / best qualities of each of the library. If you go with #2 -- your addClass' code will be at 4 times larger than the ones provided by any of the libraries, since for example when Dojo is included, you'll have to write the code for the function as the first param (jQuery) and the Object as the first param (MooTools).

Therefore, although it is theoretically possible, it isn't practical, but is a very nice way to understand the intricacies of the libraries out there.