TracyGJG/Enumerate

A utility for the generation of Enumated values

Enumerate

A utility for the generation of Enumated values

Use Cases

1. Convert literal constants into reference values.
2. Creation of function maps as an alternative to using switch/case blocks.
3. Generate a set of ordinal values.

The module is supplied as the default export of the library, so can be given a name appropriate to the context of use but, for our purposes, we will assume the module will be imported as Enumerate.

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Conversion of literal constants

Instead of something like:

confirmationDialog.visible = true;

we want to be able to use:

confirmationDialog.visible = Dialog.SHOW;

This would mean, should the underlying implmentation of the dialog changed and the expected value of the visible property change from Boolean to a number (true => 1, false => 0), only the constant reference need reflect the change.

To create the Dialog enumeration we use the following call:

const Dialog = Enumerate.constants({
  SHOW: true,
  HIDE: false,
});

Ideally, the constants method will also ensure the values of SHOW and HIDE could not be changed usign the Object.freeze method.

The names of the generated constants will be reformatted if they contain lowercase characters. E.g. hideDialog will become HIDE_DIALOG.

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Creation of function maps

Most programming languages have a multiple-choice structure such as the switch/case statements in JavaScript. Whilst there is nothing intrinsically wrong with the mechanism there is potential for errors to arise if not implemented properly or poorly maintained. However, when case values map to specific functions many of these issues can often be avoided through the use of a function map.

The Enumerate.functionMap method provides a convenient mechanism for constructing a function map with a fallback should a supplied value fail to map.

const mockFallback = _ => _;

const mappedFunctions = Enumerate.functionMap(
  {
    worked: _ => _.toUpperCase(),
  },
  mockFallback
);

mappedFunctions('worked')('test'); // TEST

mappedFunctions('failed')('test'); // test

If no fallback is provided and mapping not achieved an exception will be thrown to indicate what value was attempted.

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Generate a set of ordinal values

A very common construct in software is a collection of ordinal values. A set of constants with predefined and fixed values such as days of the week or months of the year.

const DAYS_OF_THE_WEEK = Enumerate.ordinals([
  'Mon',
  'Tue',
  'Wed',
  'Thu',
  'Fri',
  'Sat',
  'Sun',
]);

console.log(DAYS_OF_THE_WEEK.WED < DAYS_OF_THE_WEEK.MON); // false
console.log(DAYS_OF_THE_WEEK.WED < DAYS_OF_THE_WEEK.FRI); // true

The ordinals method will apply a zero-based increamental value by default but this can be overridden by providing a mapping function as the second parameter.

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