Code that adheres to OCP

adheres-to-ocp.js

  class Circle {
    constructor (radius) {
      this.radius = radius
    }

    area () {
      return 2 * Math.PI * Math.pow(shape.radius, 2)
    }
  }

  class Square {
    constructor (length) {
      this.length = length
    }

    area () {
      return Math.pow(shape.length, 2) 
    }
  }

  class AreaCalculator {
    constructor (shapes) {
      this.shapes = shapes
    }

    sum () {
      return this.shapes
        .map((shape) => {
          if (typeof shape.area === 'function') {
            return shape.area()
          } else {
            throw new Error('The area you supplied does not conform to the area interface')
          }
        })
        .reduce((totalArea, currentArea) => {
          return totalArea + currentArea
        }, 0)
    }
  }