VeilObjects

The JS/TS implementation of Veil objects approach from EO oriented programming

Notice that the package is under active development currently.

Objectives

See original paper which this package idea is based upon - https://www.yegor256.com/2020/05/19/veil-objects.html

The objective is to use the EO oriented programming, so called: "Veil objects" approach in JS/TS

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Contributing

See all you need here: https://gadzhievislam.org/Programming/Contributing

Issues

You're welcome to submit any issues related to existing issues tags, and start to work on existing.

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Usage

The veil object wraps a target object with provided presets object and when trying to access the provided presets methods on the veil object - it passes them through, until the veil object is pierced, meaning some methods were invoked that are not listed in the provided preset object.

See the example below (in TypeScript for type illustration purposes):

// Create a Project class with dynamic methods

type TDBFetcher = (field: string, id: number) => string;

class Project {
  constructor(
    private readonly dataFetcher: TDBFetcher,
    private readonly id: number
  ) {
    this.dataFetcher = dataFetcher;
    this.id = id;
  }

  name(): string {
    return this.dataFetcher("name", this.id);
  }

  author(): string {
    return this.dataFetcher("author", this.id);
  }

  description(): string {
    return this.dataFetcher("description", this.id);
  }
};

Now let's try to use our Veil object:

JavaScript

const veiledProject = new Veil(
  new Project(fetchData, 1),
  { name: 'project-1', author: 'Alex' },
);

// Call methods on the veiled object
console.log( veiledProject.name() ); // Outputs: "project-1" (preset value)
console.log( veiledProject.author() ); // Outputs: "Alex" (preset value)

// Accessing a non-preset method pierces the Veil
console.log( veiledProject.description() ); // Pierces the veil and fetches from `project`

// Now fetches via target object native method: `project.name()`, no longer uses preset
// Outputs: "project.name()", wher `project` is `new Project()` from the Veil target
console.log( veiledProject.name() );

TypeScript

const veiledProject = new Veil(
  new Project(fetchData, 1),
  { name: 'project-1', author: 'Alex' },
) as unknown as Project;

// As you might've witnessed a nuance for using with TypeScript:
// The only way to infer the target object types from the dynamic nature of Veil class for TypeScript
// is to use type casting with - `as unkown as <targetType>`.
//
// That's why it's strongly recommended to either:
// - Use the Veil only in JS code
// - Find some workarounds for TS

Tests

Test cases, Test results