In computer programming, the specification pattern is a particular software design pattern, whereby business rules can be recombined by chaining the business rules together using boolean logic.

-- Wikipedia.org ( https://en.wikipedia.org/wiki/Specification_pattern )

To use ts-specification with Node just run:

npm install ts-specification

and import the package afterwards:

import Specification from 'ts-specification'

The test cases are written in JavaScript and can be tested with:

npm test

To create custom specifications just extend from the CompositeSpecification class and implement the isSatisfiedBy function.

TypeScript

class RangeSpecification<T> extends CompositeSpecification<T> {

  private a: T
  private b: T

  constructor(a: T, b: T) {
      super()
      this.a = a
      this.b = b
  }

  isSatisfiedBy(candidate: T): boolean {
      return candidate >= this.a && candidate <= this.b
  }
}

JavaScript

import {CompositeSpecification} from 'ts-specification';

class TrueSpecification extends CompositeSpecification {

    isSatisfiedBy(candidate) {
        return true;
    }
}