Creating Node.js enum in code to match list of values in database

Question

I have a list of valid values that I am storing in a data store. This list is about 20 items long now and will likely grow to around 100, maybe more.

I feel there are a variety of reasons it makes sense to store this in a data store rather than just storing in code. I want to be able to maintain the list and its metadata and make it accessible to other services, so it seems like a micro-service data store.

But in code, we want to make sure only values from the list are passed, and they can typically be hardcoded. So we would like to create an enum that can be used in code to ensure that valid values are passed.

I have created a simple node.js that can generate a JS file with the enum right from the data store. This could be regenerated anytime the file changes or maybe on a schedule. But sharing the enum file with any node.js applications that use it would not be trivial.

Has anyone done anything like this? Any reason why this would be a bad approach? Any feedback is welcome.

Use https://github.com/rauschma/enumify it for this type of small pattern and go for the next big stuff. — Paresh Barad, May 21 '19 at 13:58
@PareshBarad yes I have been using an enum library--enum for node. https://github.com/adrai/enum But I feel like the actual enum is probably the easy part. — John Tabernik, May 21 '19 at 15:05

Tim Klein · Answer 1 · 2019-05-22T13:22:50.263

3

Piggy-backing off of this answer, which describes a way of creating an "enum" in JavaScript: you can grab the list of constants from your server (via an HTTP call) and then generate the enum in code, without the need for creating and loading a JavaScript source file.

Given that you have loaded your enumConstants from the back-end (here I hard-coded them):

const enumConstants = [
    'FIRST',
    'SECOND',
    'THIRD'
];

const temp = {};

for (const constant of enumConstants) {
    temp[constant] = constant;
}

const PlaceEnum = Object.freeze(temp);

console.log(PlaceEnum.FIRST);

// Or, in one line
const PlaceEnum2 = Object.freeze(enumConstants.reduce((o, c) => { o[c] = c; return o; }, {}));

console.log(PlaceEnum2.FIRST);

It is not ideal for code analysis or when using a smart editor, because the object is not explicitly defined and the editor will complain, but it will work.

edited May 22 '19 at 13:22

answered May 21 '19 at 13:44

Tim Klein

2,538
15
19

@DanielOrmeño - That one-liner does not work for this. That maps to a list of objects, like so: `[ { FIRST: 'FIRST' }, { SECOND: 'SECOND' }, { THIRD: 'THIRD' } ]`. – Tim Klein May 22 '19 at 13:14
Oops, you are 100% correct. I jumped the gun there I've fixed the comment. – Daniel Ormeño May 22 '19 at 13:29
1

Here's the /correct/ one liner for this `Object.freeze(enumConstants.reduce((a, c) => ({...a, [c]: c}), {}))` – Daniel Ormeño May 22 '19 at 13:30
That is a little inefficient, as it creates a new object literal for every constant. See my updated answer for a better approach which simply adds keys to the existing enum object in the reduce operation. – Tim Klein May 22 '19 at 13:32
1

Agreed! NIce observation on efficiency. – Daniel Ormeño May 22 '19 at 13:37

score 1 · Answer 2 · answered May 21 '19 at 18:44

Another approach is just to use an array and look for its members.

const members = ['first', 'second', 'third'...]

// then test for the members
members.indexOf('first') // 0
members.indexOf('third') // 2
members.indexOf('zero') // -1
members.indexOf('your_variable_to_test') // does it exist in the "enum"?

Any value that is >=0 will be a member of the list. -1 will not be a member. This doesn't "lock" the object like freeze (above) but I find it suffices for most of my similar scenarios.

Creating Node.js enum in code to match list of values in database

2 Answers2