freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/object-oriented-programming/understand-own-properties.english.md

id, title, challengeType

id	title	challengeType
587d7dae367417b2b2512b7b	Understand Own Properties	1

Description

In the following example, the Bird constructor defines two properties: name and numLegs:

function Bird(name) {
  this.name  = name;
  this.numLegs = 2;
}

let duck = new Bird("Donald");
let canary = new Bird("Tweety");

name and numLegs are called own properties, because they are defined directly on the instance object. That means that duck and canary each has its own separate copy of these properties. In fact every instance of Bird will have its own copy of these properties. The following code adds all of the own properties of duck to the array ownProps:

let ownProps = [];

for (let property in duck) {
  if(duck.hasOwnProperty(property)) {
    ownProps.push(property);
  }
}

console.log(ownProps); // prints [ "name", "numLegs" ]

Instructions

Add the own properties of canary to the array ownProps.

Tests

tests:
  - text: <code>ownProps</code> should include the values <code>"numLegs"</code> and <code>"name"</code>.
    testString: assert(ownProps.indexOf('name') !== -1 && ownProps.indexOf('numLegs') !== -1);
  - text: Solve this challenge without using the built in method <code>Object.keys()</code>.
    testString: assert(!/Object(\.keys|\[(['"`])keys\2\])/.test(code));
  - text: Solve this challenge without hardcoding the <code>ownProps</code> array.
    testString: assert(!/\[\s*(?:'|")(?:name|numLegs)|(?:push|concat)\(\s*(?:'|")(?:name|numLegs)/.test(code));

Challenge Seed

function Bird(name) {
  this.name = name;
  this.numLegs = 2;
}

let canary = new Bird("Tweety");
let ownProps = [];
// Add your code below this line

Solution

function Bird(name) {
  this.name = name;
  this.numLegs = 2;
}

let canary = new Bird("Tweety");
function getOwnProps (obj) {
  const props = [];

  for (let prop in obj) {
    if (obj.hasOwnProperty(prop)) {
      props.push(prop);
    }
  }

  return props;
}

const ownProps = getOwnProps(canary);