freeCodeCamp

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id	title	challengeType
587d7db2367417b2b2512b8a	Use Closure to Protect Properties Within an Object from Being Modified Externally	1

Description

In the previous challenge, bird had a public property name. It is considered public because it can be accessed and changed outside of bird's definition.

bird.name = "Duffy";

Therefore, any part of your code can easily change the name of bird to any value. Think about things like passwords and bank accounts being easily changeable by any part of your codebase. That could cause a lot of issues. The simplest way to make properties private is by creating a variable within the constructor function. This changes the scope of that variable to be within the constructor function versus available globally. This way, the property can only be accessed and changed by methods also within the constructor function.

function Bird() {
  let hatchedEgg = 10; // private property

  this.getHatchedEggCount = function() { // publicly available method that a bird object can use
    return hatchedEgg;
  };
}
let ducky = new Bird();
ducky.getHatchedEggCount(); // returns 10

Here getHachedEggCount is a privileged method, because it has access to the private variable hatchedEgg. This is possible because hatchedEgg is declared in the same context as getHachedEggCount. In JavaScript, a function always has access to the context in which it was created. This is called closure.

Instructions

Change how weight is declared in the Bird function so it is a private variable. Then, create a method getWeight that returns the value of weight.

Tests

tests:
  - text: The <code>weight</code> property should be a private variable.
    testString: 'assert(!code.match(/this\.weight/g), ''The <code>weight</code> property should be a private variable.'');'
  - text: Your code should create a method in <code>Bird</code> called <code>getWeight</code> that returns the <code>weight</code>.
    testString: 'assert((new Bird()).getWeight() === 15, ''Your code should create a method in <code>Bird</code> called <code>getWeight</code> that returns the <code>weight</code>.'');'

Challenge Seed

function Bird() {
  this.weight = 15;
  
  
}

Solution

function Bird() {
  let weight = 15;
  
  this.getWeight = () => weight;
}

2.8 KiB Raw Blame History