Angular dependency injection: why?

At work we teach and consult on various topics, notably (for this post) Angular. We are often asked why Angular has and heavily uses dependency injection. Here are my answers to this question; I haven’t had a chance to compare notes with the rest of our Angular expert team, so here it is, on my personal blog. (However, special thanks to Paul Spears, who helped clarify these ideas.)

Dependency injection has a considerable complexity cost, so it’s important to have good reasons to add this complexity to a framework or application. There are an unlimited number of potential features and patterns to follow, so the default for any particular feature or pattern must be “no”. Moreover, popular Angular alternatives (like React) thrive without a dependency injection system, constituting an “existence proof” that it is not a necessity, but rather a choice.

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Adjust base href via a NPM package.json scripts

Suppose you wanted to adjust the base HREF in an index.html file using a regular expression, as part of a build process you are cobbling together using NPM scripts. How could you do that? Here’s one answer, though this only works if the sed command line tool is available (as it will be almost always on Linux or Mac, and only if you install it on Windows):

Unfortunately, I have begged a question. (In the traditional sense and that I assumed an answer to a question, not the modern repurposed thing of the phrase). Is it actually a good idea to use the combination of a regular expression and a script written in a JSON file, to do anything at all?

Looking at the multiple levels of \\/\/\/\\\///\// escaping above, I think the answer to this question is clearly no. It would be better to use some other means for this adjustment. On other projects we have done the same manipulation using a tool that manipulates the HTML structure. It is more verbose but vastly easier to understand.

(Incidentally, I used to do things somewhat like the above to adjust the base URLs for Angular applications.   This is not necessary anymore if using Angular CLI  – it has an option built in, –base-href.)



AngularJS Training

Over at work, we’re re-launching a line of business from some years ago: training. Specifically, an Angular “Boot Camp” course to help developers become productive in some powerful but daunting tool.

Why? Because we think AngularJS (and its competitors like Ember) are an important step forward in how complex “single-page” web applications are constructed. The AngularJS approach is not the only good way to build such applications (for example, over in the Clojure space, Pedestal is genius; elsewhere in JavaScript, Facebook React is very appealing). But AngularJS is popular, growing fast, and suitable for many application needs.