October 28, 2014

(Special thanks to [@joliv](https://twitter.com/_joliv), @sgianazza and @rafaelchiti for reviewing and sending feedback.)_

For the past two years or so I’ve been developing in my full time job with Angular for client side Javascript. While I love learning new stuff, I was never sold on it. I didn’t use it in my personal, fun or freelance projects where the tech stack was for me to choose.

This post is to write down what I, after said two years, found that’s wrong about this framework. I’m doing this to have my thoughts clearly written down and be as objective as I can possibly be when it comes to choosing a library/framework. Also I hope someone would read this so that she can follow this advise, or not, but at least we can discuss about it. I truly believe that despite being the (currently) most popular framework out there, it is not the best choice you could make.

Ok let’s start with this!

Angular embraces mutability

Almost everything in Angular revolves around keeping references to things. You don’t have to modify those references, otherwise Angular won’t keep track of the same object and it won’t detect changes on the lost one anymore. In order for angular to do its job, it expects you to mutate the object that is being referenced, so that its digest cycle can track the changes.

And why this is bad you say?

Well, to start with, you need to keep a mental reference of the current state of the app. When mutating things around, you need to think about mutation order, because you may get different results based on the intermediate states and you cannot track where the change comes from very easily, since references can be kept anywhere and can be mutated freely. This doesn’t happen with immutable data, since you always have read-only values with functions that return new objects whenever you perform an action on them. So mutations in other contexts will only create new read-only values, which will not interfere with the one you’re working with at a given place. This has a simpler mental footprint and is easier to think about when looking at different parts of your code.

Another disadvantage is that it is harder to test. Mutations are imperative, they are a set of instructions to make your code go from state A to state B. Since you write the transition code yourself, you need to test that if you want to be confident on the outcome of it. The number of transitions grows (worst case) quadratically depending on the number of states your app has. Testing that amount of different paths just doesn’t scale.

One last disadvantage is expensive diffing checks, since it involves having to test all the properties of two given objects to see if any one is different. With immutables, you can be sure that if the references are the same, the object didn’t change, which is the most common case.

There are a lot more, but you get the idea.

Scope inheritance design is flawed

Have you ever had this issue?

In case you don’t want to go to the link and read:

“…Scope inheritance is normally straightforward, and you often don’t even need to know it is happening… until you try 2-way data binding (i.e., form elements, ng-model) to a primitive (e.g., number, string, boolean) defined on the parent scope from inside the child scope. It doesn’t work the way most people expect it should work. What happens is that the child scope gets its own property that hides/shadows the parent property of the same name…”

That problem is due to how scope inheritance works, which relies on normal prototype inheritance. So some may claim it is not a bug in Angular, it is how prototypical inheritance works. But I say that the fact this happens to every developer from time to time, be it new or experienced, is a problem with Angular, since it chose that API to interact with developers. It is actually such a common problem that it has its place in the Angular wiki (the previous link).

If all developers step into the same problem when using some specific API, then there is a problem with that API. There is something that is not well thought of, and can (and should) be improved. Choosing an inheritance chain with scopes and having to know which directive causes a new scope to be created and which not, is not a particularly good API.

Directives are too low level

The directive linking function is like an all-inclusive hotel in the Caribbean: you can do pretty much anything you want. But also, you’re left on your own. You have this place to manipulate the DOM, manipulate the scope, manipulate services, interact with the associated controller, do transclusion, and whatnot. Given that there is no middle-ground abstraction to create custom components other than this, this is way too low level and leaves you pretty much with no clue of what to do here. It’s like an empty sheet of paper. Sometimes it’s easier to have something written and work from that, than to start on your own.

I think the directive API should have some intermediate ways to do the common-case, in a simpler way than the current API provides.

Too many ways to define a service

Factories, Providers, Services, Values, Constants. Too many ways to define injectable components. You almost always use factories and values, and in some more complex cases you need some startup code and use a provider. In those cases you may also need to use a constant. Services are just too specific and never had to use them in my entire experience with angular.

In any case, there are way too many choices and if you’re not an experienced developer with the framework you may end up confused with what you need to use in your particular case. After all, you just need to create an object, and if you want it to be a factory, it’s not that hard to do one by hand, isnt’ it?

Reimplements modules instead of embracing existing ones

Angular implements its own module system for tracking dependencies between components. It is a good thing when using angular on its own, or without any module system, but when you want to use one, you are redundantly wrapping angular modules in CommonJS or AMD modules to make them work in the rest of your app. Also, you cannot define dependencies other than other angular components in this way, so you get a solution that reinvents the wheel but only for its own needs.

I think it would be wiser to embrace the existing work and be friendlier with code that lives outside angular.

Dirty checking the model data does not scale

Angular starts to get slow when there are more than 2000 bindings in your page. It is true that more than 2000 pieces of information at the same time are no good for humans to see, but the truth is that angular binding is not dependent on the visible elements on the page, but on the amount of data being watched on it. There may be a lot more watches of data than elements being shown, and that’s the actual problem with angular. It dirty checks on the data.

Some other solutions, like React, do dirty checking at the view level, by diffing the DOM state using lightweight representations of it. This is way more performant, since this doesn’t depend on how much data you have, and it is directly proportional on the amount of DOM elements you have in your page, which directly corresponds to how well you design your pages for humans to use.

API is halfway there

Have you seen how the directive API looks in angular?

return { restrict : 'EAC' , require : '^?parentDirective' , scope : { foo : '=' , bar : '&theBar' , baz : '@someBaz' } } ;

This is so cryptic. You need to rely on special characters, symbols and conventions in between to see what that actually does. That is not a good sign of a clear, easy to use API. Same thing goes for the syntax of ngOptions and ngRepeat , for which I always need some documentation lookup to see how to structure the expression. Again, not clear.

Too many ways to do the same thing, no best way to do it

Angular provides a lot of ways to do the same thing, like different kinds of services (we saw that before). There’s also several ways to use a directive (element, attribute, class, comment, same scope, no scope, isolated scope), and several ways to use a controller. You can expose your controller functions using controller-as , or you can just use normal controllers with an injected scope.

All this adds into complexity, learning curve for new developers, lack of conventions, and lack of best practices to enforce. This is bad for the ecosystem around angular, both user-developers and library-developers.

No clear way to tell behavior from the html

Directives go into your html. They can be declared as tags, attributes, classes (huh?) or even comments (whattt???). This makes it really hard to tell a normal attribute versus a directive, and you’re no longer safe (or comfortable at least) to change the html, since you could be removing a directive or a directive parameter without notice.

This is a really dangerous way to work. Comments and css classes shouldn’t be allowed by angular to start with, but some more thought should be done when designing your app and make directives as clear as possible, since the html becomes the API for them, so you should make that API clear for the user, which may or may not be yourself. And even when you get that part clear, there’s still some other details that are not clear to the user. Like the type of scope the directive uses (isolated, no scope?, same scope?), whether it depends on some upper value in the scope, and stuff like that. It doesn’t have a clear layer where your data is safely hidden from.

Cannot be used to run server side in a decent way

Angular needs a DOM to work. This is unlike other approaches where string templates are used, or even a virtual representation of the DOM that is not coupled to an existing DOM. And in the server we don’t have a DOM available. At least not a real one. We have some libraries that create DOM structures that claim to be compatible, and they may be up to some extent, but they won’t be exactly the DOM that angular needs.

One approach for rendering server side with angular is by using a headless browser to execute angular and then get the rendered html from there. That is not an optimal solution since it requires a browser to be up and running, which causes a lot of overhead to the request.

You need to use low level APIs really soon

A good practice in angular is to break up your app into modular directives with specific functionality. In those places, you need to couple with both the scope and the DOM. If you do anything beyond trivial, you’ll find yourself starting to use $apply because you’ll be outside the context where angular knows what to do. Especially if you start using external plugins that manipulate the DOM.

Also, both in directives and in controllers, if you really want to react to changes in the data and not rely on the view calling you to update based on changes of the input models, you’ll start using $watch a lot too. While this is not complex at all, and it’s not hard to reason (though it’s easy to cause loops if you update state when watching changes that trigger other watches and so on), you get out of the simple and wonderful land where angular does the job for you, and you need to keep telling angular what to do.

It’s as if angular was a magician, but one that likes to reveal its tricks as soon as it shows them to you.

Performance improvements are too granular, and not at the correct points

ngModelOptions is a directive option that allows you to reduce the number of digests to be done on the model attached to it. But really? I need to do performance optimization in the view template? Isn’t there some kind of place I can hook to add an optimization, which is not invasive and is in a clear, explicit way where I can see it? Or even a way to apply global optimizations?

Performance should be a secondary thing to do with your app. So good performance strategies are ones that are applied as cross cutting concerns, or be configuration options of the library, or hooks.

It’s ok to have some performance optimizations inlined in the code in some particular cases, but let’s at least not put those in the html, the most brittle place in your app. Views should remain logic less and unaware of performance optimizations as much as possible.

Conclusion

For all the above reasons, and some other subjective ones that I didn’t write here because they are, well, subjective, I don’t recommend angular as the tool to use when building interactive UIs. There are much better alternatives, that have a much richer philosophy and strong concepts. One big example of this is React. I suggest that you give it a chance and see what it has to offer.