freeCodeCamp/curriculum/challenges/02-javascript-algorithms-and-data-structures/object-oriented-programming/Make Code More Reusable with the this Keyword.md

id, title, challengeType

id	title	challengeType
587d7dad367417b2b2512b76	Make Code More Reusable with the this Keyword	1

Description

The last challenge introduced a method to the duck object. It used duck.name dot notation to access the value for the name property within the return statement: sayName: function() {return "The name of this duck is " + duck.name + ".";} While this is a valid way to access the object's property, there is a pitfall here. If the variable name changes, any code referencing the original name would need to be updated as well. In a short object definition, it isn't a problem, but if an object has many references to its properties there is a greater chance for error. A way to avoid these issues is with the this keyword:

let duck = {
  name: "Aflac",
  numLegs: 2,
  sayName: function() {return "The name of this duck is " + this.name + ".";}
};

this is a deep topic, and the above example is only one way to use it. In the current context, this refers to the object that the method is associated with: duck. If the object's name is changed to mallard, it is not necessary to find all the references to duck in the code. It makes the code reusable and easier to read.

Instructions

Modify the dog.sayLegs method to remove any references to dog. Use the duck example for guidance.

Tests

- text: <code>dog.sayLegs()</code> should return the given string.
  testString: 'assert(dog.sayLegs() === "This dog has 4 legs.", "<code>dog.sayLegs()</code> should return the given string.");'
- text: Your code should use the <code>this</code> keyword to access the <code>numLegs</code> property of <code>dog</code>.
  testString: 'assert(code.match(/this\.numLegs/g), "Your code should use the <code>this</code> keyword to access the <code>numLegs</code> property of <code>dog</code>.");'

Challenge Seed

let dog = {
  name: "Spot",
  numLegs: 4,
  sayLegs: function() {return "This dog has " + dog.numLegs + " legs.";}
};

dog.sayLegs();

Solution

let dog = {
  name: "Spot",
  numLegs: 4,
  sayLegs () {
    return 'This dog has ' + this.numLegs + ' legs.';
  }
};

dog.sayLegs();