├── .github
├── dependabot.yml
└── workflows
│ └── ci.yml
├── .gitignore
├── CONTRIBUTING.md
├── LICENSE
├── README.md
├── elmish.md
├── index.html
├── lib
├── elmish.js
├── favicon.ico
├── server.js
├── test.js
├── todo-app.js
├── todo.html
├── todomvc-app.css
└── todomvc-common-base.css
├── package-lock.json
├── package.json
└── test
├── counter-reset-keyboard.js
├── counter.js
├── elmish.test.js
└── todo-app.test.js
/.github/dependabot.yml:
--------------------------------------------------------------------------------
1 | version: 2
2 | updates:
3 | - package-ecosystem: npm
4 | directory: "/"
5 | schedule:
6 | interval: monthly
7 | time: "17:00"
8 | timezone: Europe/London
9 |
--------------------------------------------------------------------------------
/.github/workflows/ci.yml:
--------------------------------------------------------------------------------
1 | # This workflow will do a clean install of node dependencies, cache/restore them, build the source code and run tests across different versions of node
2 | # For more information see: https://help.github.com/actions/language-and-framework-guides/using-nodejs-with-github-actions
3 |
4 | name: Node.js CI
5 |
6 | on:
7 | push:
8 | branches: [ main ]
9 | pull_request:
10 | branches: [ main ]
11 |
12 | jobs:
13 | build:
14 |
15 | runs-on: ubuntu-latest
16 |
17 | strategy:
18 | matrix:
19 | node-version: [22.x, 24.x]
20 | # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
21 |
22 | steps:
23 | - uses: actions/checkout@v4
24 | - name: Use Node.js ${{ matrix.node-version }}
25 | uses: actions/setup-node@v4
26 | with:
27 | node-version: ${{ matrix.node-version }}
28 | cache: 'npm'
29 | - run: npm ci
30 | # - run: npm run build --if-present
31 | - run: npm test
32 | - name: Upload coverage to Codecov
33 | uses: codecov/codecov-action@v5
34 |
--------------------------------------------------------------------------------
/.gitignore:
--------------------------------------------------------------------------------
1 | # Logs
2 | logs
3 | *.log
4 | npm-debug.log*
5 |
6 | # Runtime data
7 | pids
8 | *.pid
9 | *.seed
10 | *.pid.lock
11 |
12 | # Directory for instrumented libs generated by jscoverage/JSCover
13 | lib-cov
14 |
15 | # Coverage directory used by tools like istanbul
16 | coverage
17 |
18 | # nyc test coverage
19 | .nyc_output
20 |
21 | # Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
22 | .grunt
23 |
24 | # Bower dependency directory (https://bower.io/)
25 | bower_components
26 |
27 | # node-waf configuration
28 | .lock-wscript
29 |
30 | # Compiled binary addons (https://nodejs.org/api/addons.html)
31 | build/Release
32 |
33 | # Dependency directories
34 | node_modules/
35 | jspm_packages/
36 |
37 | # TypeScript v1 declaration files
38 | typings/
39 |
40 | # Optional npm cache directory
41 | .npm
42 |
43 | # Optional eslint cache
44 | .eslintcache
45 |
46 | # Optional REPL history
47 | .node_repl_history
48 |
49 | # Output of 'npm pack'
50 | *.tgz
51 |
52 | # dotenv environment variables file
53 | .env
54 |
55 | # next.js build output
56 | .next
57 |
--------------------------------------------------------------------------------
/CONTRIBUTING.md:
--------------------------------------------------------------------------------
1 | _**Please read** our_ [**contribution guide**](https://github.com/dwyl/contributing) (_thank you_!)
2 |
--------------------------------------------------------------------------------
/LICENSE:
--------------------------------------------------------------------------------
1 | GNU GENERAL PUBLIC LICENSE
2 | Version 2, June 1991
3 |
4 | Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
5 | 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
6 | Everyone is permitted to copy and distribute verbatim copies
7 | of this license document, but changing it is not allowed.
8 |
9 | Preamble
10 |
11 | The licenses for most software are designed to take away your
12 | freedom to share and change it. By contrast, the GNU General Public
13 | License is intended to guarantee your freedom to share and change free
14 | software--to make sure the software is free for all its users. This
15 | General Public License applies to most of the Free Software
16 | Foundation's software and to any other program whose authors commit to
17 | using it. (Some other Free Software Foundation software is covered by
18 | the GNU Lesser General Public License instead.) You can apply it to
19 | your programs, too.
20 |
21 | When we speak of free software, we are referring to freedom, not
22 | price. Our General Public Licenses are designed to make sure that you
23 | have the freedom to distribute copies of free software (and charge for
24 | this service if you wish), that you receive source code or can get it
25 | if you want it, that you can change the software or use pieces of it
26 | in new free programs; and that you know you can do these things.
27 |
28 | To protect your rights, we need to make restrictions that forbid
29 | anyone to deny you these rights or to ask you to surrender the rights.
30 | These restrictions translate to certain responsibilities for you if you
31 | distribute copies of the software, or if you modify it.
32 |
33 | For example, if you distribute copies of such a program, whether
34 | gratis or for a fee, you must give the recipients all the rights that
35 | you have. You must make sure that they, too, receive or can get the
36 | source code. And you must show them these terms so they know their
37 | rights.
38 |
39 | We protect your rights with two steps: (1) copyright the software, and
40 | (2) offer you this license which gives you legal permission to copy,
41 | distribute and/or modify the software.
42 |
43 | Also, for each author's protection and ours, we want to make certain
44 | that everyone understands that there is no warranty for this free
45 | software. If the software is modified by someone else and passed on, we
46 | want its recipients to know that what they have is not the original, so
47 | that any problems introduced by others will not reflect on the original
48 | authors' reputations.
49 |
50 | Finally, any free program is threatened constantly by software
51 | patents. We wish to avoid the danger that redistributors of a free
52 | program will individually obtain patent licenses, in effect making the
53 | program proprietary. To prevent this, we have made it clear that any
54 | patent must be licensed for everyone's free use or not licensed at all.
55 |
56 | The precise terms and conditions for copying, distribution and
57 | modification follow.
58 |
59 | GNU GENERAL PUBLIC LICENSE
60 | TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
61 |
62 | 0. This License applies to any program or other work which contains
63 | a notice placed by the copyright holder saying it may be distributed
64 | under the terms of this General Public License. The "Program", below,
65 | refers to any such program or work, and a "work based on the Program"
66 | means either the Program or any derivative work under copyright law:
67 | that is to say, a work containing the Program or a portion of it,
68 | either verbatim or with modifications and/or translated into another
69 | language. (Hereinafter, translation is included without limitation in
70 | the term "modification".) Each licensee is addressed as "you".
71 |
72 | Activities other than copying, distribution and modification are not
73 | covered by this License; they are outside its scope. The act of
74 | running the Program is not restricted, and the output from the Program
75 | is covered only if its contents constitute a work based on the
76 | Program (independent of having been made by running the Program).
77 | Whether that is true depends on what the Program does.
78 |
79 | 1. You may copy and distribute verbatim copies of the Program's
80 | source code as you receive it, in any medium, provided that you
81 | conspicuously and appropriately publish on each copy an appropriate
82 | copyright notice and disclaimer of warranty; keep intact all the
83 | notices that refer to this License and to the absence of any warranty;
84 | and give any other recipients of the Program a copy of this License
85 | along with the Program.
86 |
87 | You may charge a fee for the physical act of transferring a copy, and
88 | you may at your option offer warranty protection in exchange for a fee.
89 |
90 | 2. You may modify your copy or copies of the Program or any portion
91 | of it, thus forming a work based on the Program, and copy and
92 | distribute such modifications or work under the terms of Section 1
93 | above, provided that you also meet all of these conditions:
94 |
95 | a) You must cause the modified files to carry prominent notices
96 | stating that you changed the files and the date of any change.
97 |
98 | b) You must cause any work that you distribute or publish, that in
99 | whole or in part contains or is derived from the Program or any
100 | part thereof, to be licensed as a whole at no charge to all third
101 | parties under the terms of this License.
102 |
103 | c) If the modified program normally reads commands interactively
104 | when run, you must cause it, when started running for such
105 | interactive use in the most ordinary way, to print or display an
106 | announcement including an appropriate copyright notice and a
107 | notice that there is no warranty (or else, saying that you provide
108 | a warranty) and that users may redistribute the program under
109 | these conditions, and telling the user how to view a copy of this
110 | License. (Exception: if the Program itself is interactive but
111 | does not normally print such an announcement, your work based on
112 | the Program is not required to print an announcement.)
113 |
114 | These requirements apply to the modified work as a whole. If
115 | identifiable sections of that work are not derived from the Program,
116 | and can be reasonably considered independent and separate works in
117 | themselves, then this License, and its terms, do not apply to those
118 | sections when you distribute them as separate works. But when you
119 | distribute the same sections as part of a whole which is a work based
120 | on the Program, the distribution of the whole must be on the terms of
121 | this License, whose permissions for other licensees extend to the
122 | entire whole, and thus to each and every part regardless of who wrote it.
123 |
124 | Thus, it is not the intent of this section to claim rights or contest
125 | your rights to work written entirely by you; rather, the intent is to
126 | exercise the right to control the distribution of derivative or
127 | collective works based on the Program.
128 |
129 | In addition, mere aggregation of another work not based on the Program
130 | with the Program (or with a work based on the Program) on a volume of
131 | a storage or distribution medium does not bring the other work under
132 | the scope of this License.
133 |
134 | 3. You may copy and distribute the Program (or a work based on it,
135 | under Section 2) in object code or executable form under the terms of
136 | Sections 1 and 2 above provided that you also do one of the following:
137 |
138 | a) Accompany it with the complete corresponding machine-readable
139 | source code, which must be distributed under the terms of Sections
140 | 1 and 2 above on a medium customarily used for software interchange; or,
141 |
142 | b) Accompany it with a written offer, valid for at least three
143 | years, to give any third party, for a charge no more than your
144 | cost of physically performing source distribution, a complete
145 | machine-readable copy of the corresponding source code, to be
146 | distributed under the terms of Sections 1 and 2 above on a medium
147 | customarily used for software interchange; or,
148 |
149 | c) Accompany it with the information you received as to the offer
150 | to distribute corresponding source code. (This alternative is
151 | allowed only for noncommercial distribution and only if you
152 | received the program in object code or executable form with such
153 | an offer, in accord with Subsection b above.)
154 |
155 | The source code for a work means the preferred form of the work for
156 | making modifications to it. For an executable work, complete source
157 | code means all the source code for all modules it contains, plus any
158 | associated interface definition files, plus the scripts used to
159 | control compilation and installation of the executable. However, as a
160 | special exception, the source code distributed need not include
161 | anything that is normally distributed (in either source or binary
162 | form) with the major components (compiler, kernel, and so on) of the
163 | operating system on which the executable runs, unless that component
164 | itself accompanies the executable.
165 |
166 | If distribution of executable or object code is made by offering
167 | access to copy from a designated place, then offering equivalent
168 | access to copy the source code from the same place counts as
169 | distribution of the source code, even though third parties are not
170 | compelled to copy the source along with the object code.
171 |
172 | 4. You may not copy, modify, sublicense, or distribute the Program
173 | except as expressly provided under this License. Any attempt
174 | otherwise to copy, modify, sublicense or distribute the Program is
175 | void, and will automatically terminate your rights under this License.
176 | However, parties who have received copies, or rights, from you under
177 | this License will not have their licenses terminated so long as such
178 | parties remain in full compliance.
179 |
180 | 5. You are not required to accept this License, since you have not
181 | signed it. However, nothing else grants you permission to modify or
182 | distribute the Program or its derivative works. These actions are
183 | prohibited by law if you do not accept this License. Therefore, by
184 | modifying or distributing the Program (or any work based on the
185 | Program), you indicate your acceptance of this License to do so, and
186 | all its terms and conditions for copying, distributing or modifying
187 | the Program or works based on it.
188 |
189 | 6. Each time you redistribute the Program (or any work based on the
190 | Program), the recipient automatically receives a license from the
191 | original licensor to copy, distribute or modify the Program subject to
192 | these terms and conditions. You may not impose any further
193 | restrictions on the recipients' exercise of the rights granted herein.
194 | You are not responsible for enforcing compliance by third parties to
195 | this License.
196 |
197 | 7. If, as a consequence of a court judgment or allegation of patent
198 | infringement or for any other reason (not limited to patent issues),
199 | conditions are imposed on you (whether by court order, agreement or
200 | otherwise) that contradict the conditions of this License, they do not
201 | excuse you from the conditions of this License. If you cannot
202 | distribute so as to satisfy simultaneously your obligations under this
203 | License and any other pertinent obligations, then as a consequence you
204 | may not distribute the Program at all. For example, if a patent
205 | license would not permit royalty-free redistribution of the Program by
206 | all those who receive copies directly or indirectly through you, then
207 | the only way you could satisfy both it and this License would be to
208 | refrain entirely from distribution of the Program.
209 |
210 | If any portion of this section is held invalid or unenforceable under
211 | any particular circumstance, the balance of the section is intended to
212 | apply and the section as a whole is intended to apply in other
213 | circumstances.
214 |
215 | It is not the purpose of this section to induce you to infringe any
216 | patents or other property right claims or to contest validity of any
217 | such claims; this section has the sole purpose of protecting the
218 | integrity of the free software distribution system, which is
219 | implemented by public license practices. Many people have made
220 | generous contributions to the wide range of software distributed
221 | through that system in reliance on consistent application of that
222 | system; it is up to the author/donor to decide if he or she is willing
223 | to distribute software through any other system and a licensee cannot
224 | impose that choice.
225 |
226 | This section is intended to make thoroughly clear what is believed to
227 | be a consequence of the rest of this License.
228 |
229 | 8. If the distribution and/or use of the Program is restricted in
230 | certain countries either by patents or by copyrighted interfaces, the
231 | original copyright holder who places the Program under this License
232 | may add an explicit geographical distribution limitation excluding
233 | those countries, so that distribution is permitted only in or among
234 | countries not thus excluded. In such case, this License incorporates
235 | the limitation as if written in the body of this License.
236 |
237 | 9. The Free Software Foundation may publish revised and/or new versions
238 | of the General Public License from time to time. Such new versions will
239 | be similar in spirit to the present version, but may differ in detail to
240 | address new problems or concerns.
241 |
242 | Each version is given a distinguishing version number. If the Program
243 | specifies a version number of this License which applies to it and "any
244 | later version", you have the option of following the terms and conditions
245 | either of that version or of any later version published by the Free
246 | Software Foundation. If the Program does not specify a version number of
247 | this License, you may choose any version ever published by the Free Software
248 | Foundation.
249 |
250 | 10. If you wish to incorporate parts of the Program into other free
251 | programs whose distribution conditions are different, write to the author
252 | to ask for permission. For software which is copyrighted by the Free
253 | Software Foundation, write to the Free Software Foundation; we sometimes
254 | make exceptions for this. Our decision will be guided by the two goals
255 | of preserving the free status of all derivatives of our free software and
256 | of promoting the sharing and reuse of software generally.
257 |
258 | NO WARRANTY
259 |
260 | 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
261 | FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
262 | OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
263 | PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
264 | OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
265 | MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
266 | TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
267 | PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
268 | REPAIR OR CORRECTION.
269 |
270 | 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
271 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
272 | REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
273 | INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
274 | OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
275 | TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
276 | YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
277 | PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
278 | POSSIBILITY OF SUCH DAMAGES.
279 |
280 | END OF TERMS AND CONDITIONS
281 |
282 | How to Apply These Terms to Your New Programs
283 |
284 | If you develop a new program, and you want it to be of the greatest
285 | possible use to the public, the best way to achieve this is to make it
286 | free software which everyone can redistribute and change under these terms.
287 |
288 | To do so, attach the following notices to the program. It is safest
289 | to attach them to the start of each source file to most effectively
290 | convey the exclusion of warranty; and each file should have at least
291 | the "copyright" line and a pointer to where the full notice is found.
292 |
293 | <<<<<<< HEAD
294 |
295 | Copyright (C)
296 | =======
297 | {description}
298 | Copyright (C) {year} {fullname}
299 | >>>>>>> project-a/master
300 |
301 | This program is free software; you can redistribute it and/or modify
302 | it under the terms of the GNU General Public License as published by
303 | the Free Software Foundation; either version 2 of the License, or
304 | (at your option) any later version.
305 |
306 | This program is distributed in the hope that it will be useful,
307 | but WITHOUT ANY WARRANTY; without even the implied warranty of
308 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
309 | GNU General Public License for more details.
310 |
311 | You should have received a copy of the GNU General Public License along
312 | with this program; if not, write to the Free Software Foundation, Inc.,
313 | 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
314 |
315 | Also add information on how to contact you by electronic and paper mail.
316 |
317 | If the program is interactive, make it output a short notice like this
318 | when it starts in an interactive mode:
319 |
320 | Gnomovision version 69, Copyright (C) year name of author
321 | Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
322 | This is free software, and you are welcome to redistribute it
323 | under certain conditions; type `show c' for details.
324 |
325 | The hypothetical commands `show w' and `show c' should show the appropriate
326 | parts of the General Public License. Of course, the commands you use may
327 | be called something other than `show w' and `show c'; they could even be
328 | mouse-clicks or menu items--whatever suits your program.
329 |
330 | You should also get your employer (if you work as a programmer) or your
331 | school, if any, to sign a "copyright disclaimer" for the program, if
332 | necessary. Here is a sample; alter the names:
333 |
334 | Yoyodyne, Inc., hereby disclaims all copyright interest in the program
335 | `Gnomovision' (which makes passes at compilers) written by James Hacker.
336 |
337 | <<<<<<< HEAD
338 | , 1 April 1989
339 | =======
340 | {signature of Ty Coon}, 1 April 1989
341 | >>>>>>> project-a/master
342 | Ty Coon, President of Vice
343 |
344 | This General Public License does not permit incorporating your program into
345 | proprietary programs. If your program is a subroutine library, you may
346 | consider it more useful to permit linking proprietary applications with the
347 | library. If this is what you want to do, use the GNU Lesser General
348 | Public License instead of this License.
349 |
--------------------------------------------------------------------------------
/elmish.md:
--------------------------------------------------------------------------------
1 | # `Elm`(_ish_)
2 |
3 | 
4 |
6 |
7 | `Elm`(_ish_) is an **`Elm`**-_inspired_ `JavaScript` (**ES5**)
8 | fully functional front-end _micro_-framework from _scratch_.[1](#notes)
9 |
10 |
11 |
12 | ## _Why?_
13 |
14 | The purpose of building `Elm`(_ish_) is _not_ to "_replace_" Elm
15 | or to create [_yet another_ front-end JS framework](https://medium.com/tastejs-blog/yet-another-framework-syndrome-yafs-cf5f694ee070)!
16 |
17 | The purpose of _separating_ the `Elm`(_ish_) functions
18 | into a "micro framework" is to:
19 | **a)** **abstract** the "plumbing" so that we can
20 | ***simplify*** the Todo List application code
21 | to _just_
22 | ["**application logic**"](https://en.wikipedia.org/wiki/Business_logic).
23 | **b)** _demo_ a ***re-useable*** (_fully-tested_)
24 | "**micro-framework**" that allows us
25 | to _practice_ using The Elm Architecture ("TEA").
26 | **c)** promote the **mindset** of writing **tests _first_**
27 | and **`then`** the _least_ amount of code necessary to pass the test
28 | (_while meeting the acceptance criteria_).
29 |
30 | > _**Test** & **Document-Driven Development** is **easy** and it's **easily**
31 | one of the **best habits** to form in your software development "career".
32 | This walkthrough shows **how** you can do it **the right way**;
33 | from the **start** of a project._
34 |
35 |
36 |
37 | ## _What?_
38 |
39 | A walkthrough of creating a
40 | _fully functional front-end_ "**micro framework**" ***from scratch***.
41 |
42 | By the end of this exercise you will _understand_
43 | The Elm Architecture (TEA) _much better_
44 | because we will be analysing, documenting, testing
45 | and writing each function required
46 | to architect and render our Todo List (TodoMVC) App.
47 |
48 |
49 |
50 | ## _Who?_
51 |
52 | People who want to gain an _in-depth_ understanding
53 | of The Elm Architecture ("TEA")
54 | and thus _intrinsically_
55 | [grok](https://en.wikipedia.org/wiki/Grok) Redux/React JavaScript apps.
56 |
57 | This tutorial is intended for _beginners_ with _modest_
58 | JavaScript knowledge (_variables, functions, DOM methods & TDD_).
59 | If you have any questions or get "stuck",
60 | please open an issue:
61 | https://github.com/dwyl/learn-elm-architecture-in-javascript/issues
62 | @dwyl is a "safe space" and we are all here to help don't be shy/afraid;
63 | the _more_ questions you ask, the more you are helping yourself and _others_!
64 |
65 |
66 |
67 | ## _How_?
68 |
69 | _Before_ diving into _writing functions_ for `Elm`(_ish_),
70 | we need to consider how we are going to _test_ it.
71 | By ensuring that we follow **TDD** from the _start_ of an project,
72 | we _avoid_ having to "correct" any "**bad habits**" later.
73 |
74 | We will be using **Tape** & **`JSDOM`** for testing the functions.
75 | Tape is a _minimalist_ testing library
76 | that is _fast_ and has _everything we need_.
77 | **`JSDOM`** is a JavaScript implementation of the
78 | WHATWG DOM & HTML standards, for use with node.js.
79 | If _either_ of these tools is _unfamiliar_ to you,
80 | please see:
81 | [https://github.com/dwyl/**learn-tape**](https://github.com/dwyl/learn-tape)
82 | and
83 | [**front-end**-with-tape.md](https://github.com/dwyl/learn-tape/blob/master/front-end-with-tape.md)
84 |
85 |
86 | ### What _Can_ We _Generalise_ ?
87 |
88 | Our **first step** in creating `Elm`(_ish_)
89 | is to _re-visit_ the functions we wrote for the "counter app"
90 | and consider what _can_ be _generalised_ into
91 | an application-independent re-useable framework.
92 |
93 | > Our **rule-of-thumb** is: anything that creates (_or destroys_)
94 | a DOM element or looks like "plumbing"
95 | (_that which is common to **all apps**, e.g: "routing" or "managing state"_)
96 | is _generic_ and should thus be abstracted into the `Elm`(_ish_) framework.
97 |
98 |
99 | Recall that there are **3 parts** to the Elm Architecture:
100 | `model`, `update` and `view`.
101 | These correspond to the `M`odel, `C`ontroller and `V`iew
102 | of
103 | ["**MVC** pattern"](https://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller),
104 | which is the most _widely used_ "software architecture pattern".
105 |
106 | > **Aside**: "**software architecture**" is just a fancy way of saying
107 | "how code is **organised**" and/or how "data **flows**" through a system.
108 | Whenever you see the word "**pattern**" it just means
109 | "a bunch of experienced people have concluded that this works well,
110 | so as beginners, we don't have to think too hard (up-front)."
111 |
112 | The _reason_ Elm refers to the "**Controller**" as "***Update***" is because
113 | this name _more accurately_ reflects what the function _does_:
114 | it _updates_ the _state_ (Model) of the application.
115 |
116 | Our `update` and `view` functions will form
117 | the "**domain logic**" of our Todo List App,
118 | (_i.e. they are "**specific**" to the Todo List_)
119 | so we cannot abstract them.
120 | The `model` will be a JavaScript `Object` where the App's
121 | data (todo list items) will be stored.
122 |
123 | The `update` function is a simple `switch` statement
124 | that "decides" how to to _`update`_ the app's `model`
125 | each `case` will call a function
126 | that _belongs_ to the Todo List App.
127 |
128 | The `view` function _invokes_ several "helper" functions
129 | which create HTML ("DOM") elements e.g: ``, `