Adding support for enums

[kai zhu]

>  In Redux, there are actions, which are strings, that get passed to a reducer, which mutates the states.  My coworker and I inadvertently added the same action name, "LOADING" on the same page, but in two different files.  This led to a bug when both my modal and his search results would be loading at the same time, but since they were never both visible, we didn't catch the bug.

can you explain in code how either enum or symbols could solve your problem?  reading up on how reducers work @ https://redux.js.org/basics/reducers#handling-more-actions <https://redux.js.org/basics/reducers#handling-more-actions>, i'm guessing the problematic code looks like the following.

```js
// module spinner.js
var action = {
    type: 'LOADING',
    ...
};

// module search.js
var action = {
    type: 'LOADING',
    ...
};

// module main.js
switch (action.type) {
case 'LOADING':
    // inadverdently run both
    // spinner-loading and
    // search-result-loading actions
    ...
    break;
}
```

its not obvious to me how enums/symbols could be use in a less-complicated solution, than simply renaming action.type in your case with more descriptive names that won’t collide (e.g. 'LOADING_SPINNER', ‘LOADING_SEARCH_RESULT').

kai zhu
kaizhu256 at gmail.com



> On 10 Jun 2018, at 11:26 AM, Michael J. Ryan <tracker1 at gmail.com> wrote:
> 
> Just use symbols for your action type
> 
> On Sat, Jun 9, 2018, 14:21 Doug Wade <douglas.b.wade at gmail.com <mailto:douglas.b.wade at gmail.com>> wrote:
> Hello friends!
> 
> I had a bug the other day on my team.  We use redux <https://redux.js.org/> to manage the state on our application <https://resumes.indeed.com/>, which is maintained by a large team.  In Redux, there are actions, which are strings, that get passed to a reducer, which mutates the states.  My coworker and I inadvertently added the same action name, "LOADING" on the same page, but in two different files.  This led to a bug when both my modal and his search results would be loading at the same time, but since they were never both visible, we didn't catch the bug.  My coworker refactored his feature, and broke my feature, such that rather than displaying a spinner, we went straight to an empty results page, even when there were results.
> 
> In other languages, like the language I use most at work, Java, we would instead use a language construct called an enum <https://en.wikipedia.org/wiki/Enumerated_type> in this situation so that the two different sets of actions weren't equal to each other.  I did some research into some previous discussions on this <https://esdiscuss.org/topic/enums> topic, and it seems like the discussion has been broadly in favor of it.  I also noted that enum is a reserved keyword <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Keywords>, which indicates some intention to add enums to the language.
> 
> As such, I've spent some time working on a proposal <https://github.com/doug-wade/proposal-enum-definitions> for adding enums to ECMAScript.  It is very heavily based on the work by rauschma <https://github.com/rauschma/enums/blob/master/enums.js>, stevekinney <https://github.com/stevekinney/ecmascript-enumerations> and rwaldron <https://github.com/rwaldron/proposal-enum-definitions>.  I wasn't sure if I was using all the right words when writing the proposal, so to help express myself better, I also spent some time writing a babel plugin <https://github.com/doug-wade/babel/tree/babel-plugin-proposal-enum> that uses a polyfill <https://github.com/doug-wade/enum-polyfill> against which I've written a small test suite <https://github.com/doug-wade/enum-unit-tests> (if you would like to run them, you'll need to link the polyfill and the babel plugin into the tests).  Please do not take these as any indication of "done-ness", I wrote them to understand how I would expect an enum in javascript to behave, and am willing and eager to make changes as I get suggestions.  I do, however, feel I have done as much as I can on my own, and would like help in considering the proposal, especially whether it contains any footguns, undefined behavior, or things that would be surprising to newer developers, and helping me identify what work is to be done to make this a "real" proposal.
> 
> All the best,
> Doug Wade
> 
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