refactoring-step-1.js

class Person {
  constructor(name) {
    this._name = name
    this._courses = []
  }
  get name() {
    return this._name
  }
  get courses() {
    return this._courses.slice()
  }
  set courses(aList) {
    this._courses = aList.slice()
  }
  addCourse(aCourse) {
    this._courses.push(aCourse)
  }
  removeCourse(
    aCourse,
    fnIfAbsent = () => {
      throw new RangeError()
    }
  ) {
    const index = this._courses.indexOf(aCourse)
    if (index == -1) fnIfAbsent()
    else this._courses.splice(index, 1)
  }
}

class Course {
  constructor(name, isAdvanced) {
    this._name = name
    this._isAdvanced = isAdvanced
  }
  get name() {
    return this._name
  }
  get isAdvanced() {
    return this._isAdvanced
  }
}

// client
numAdvancedCourses = aPerson.courses.filter((c) => c.isAdvanced).length

const basicCourseNames = readBasicCourseNames(filename)
aPerson.courses = basicCourseNames.map((name) => new Course(name, false))

for (const name of readBasicCourseNames(filename)) {
  aPerson.addCourse(new Course(name, false))
}