Demonstrate private method in JavaScript constructor function.

oop-private-methods.js

'use strict'

function Car(make, model, year) {
  // public variables
  this.make = make;
  this.model = model;
  this.year = year;
  this.breakPedalIsPressed = false;

  // private variable
  var engineStartAttempts = 0;

  this.startEngine = function() {
    if (checkStartEngineRequirements()) {
      console.log('Engine started!')
      return true;
    } else { // failed requirements
      console.log('Engine start failed!')
      return false
    }
  }

  // public method, accesses public variable
  this.pressBreakPedal = function() {
    this.breakPedalIsPressed = true;
  }

  // public method, accesses public variable
  this.releaseBreakPedal = function() {
    this.breakPedalIsPressed = false;
  }

  // private methods
    var thisCar = this;

    // private method, accesses private variable
    var checkStartEngineRequirements = function() {
      console.log('engineStartAttempts: ', ++engineStartAttempts)
      return ensureBreakPedalIsPressed();
    }

    // private method, accesses public variable
    var ensureBreakPedalIsPressed = function() {
      thisCar.breakPedalIsPressed ? true : console.log('Break pedal is not pressed.')
      return thisCar.breakPedalIsPressed;
    }
}

let car = new Car('Tesla', 'Model 4', 2021);

console.log('\n')

// start the car with a failed start, then a success start.
console.log(car.startEngine())
console.log(car.pressBreakPedal())
console.log(car.startEngine())
console.log(car.releaseBreakPedal())

console.log('\n')