freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/check-if-an-object-has-a-property.english.md

id, title, challengeType

id	title	challengeType
587d7b7d367417b2b2512b1c	Check if an Object has a Property	1

Description

Now we can add, modify, and remove keys from objects. But what if we just wanted to know if an object has a specific property? JavaScript provides us with two different ways to do this. One uses the hasOwnProperty() method and the other uses the in keyword. If we have an object users with a property of Alan, we could check for its presence in either of the following ways:

users.hasOwnProperty('Alan');
'Alan' in users;
// both return true

Instructions

We've created an object, users, with some users in it and a function isEveryoneHere, which we pass the users object to as an argument. Finish writing this function so that it returns true only if the users object contains all four names, Alan, Jeff, Sarah, and Ryan, as keys, and false otherwise.

Tests

tests:
  - text: 'The <code>users</code> object only contains the keys <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code>'
    testString: 'assert("Alan" in users && "Jeff" in users && "Sarah" in users && "Ryan" in users && Object.keys(users).length === 4, "The <code>users</code> object only contains the keys <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code>");'
  - text: 'The function <code>isEveryoneHere</code> returns <code>true</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are properties on the <code>users</code> object'
    testString: 'assert(isEveryoneHere(users) === true, "The function <code>isEveryoneHere</code> returns <code>true</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are properties on the <code>users</code> object");'
  - text: 'The function <code>isEveryoneHere</code> returns <code>false</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are not properties on the <code>users</code> object'
    testString: 'assert((function() { delete users.Alan; delete users.Jeff; delete users.Sarah; delete users.Ryan; return isEveryoneHere(users) })() === false, "The function <code>isEveryoneHere</code> returns <code>false</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are not properties on the <code>users</code> object");'

Challenge Seed

let users = {
  Alan: {
    age: 27,
    online: true
  },
  Jeff: {
    age: 32,
    online: true
  },
  Sarah: {
    age: 48,
    online: true
  },
  Ryan: {
    age: 19,
    online: true
  }
};

function isEveryoneHere(obj) {
  // change code below this line

  // change code above this line
}

console.log(isEveryoneHere(users));

Solution

function isEveryoneHere(obj) {
  return [
    'Alan',
    'Jeff',
    'Sarah',
    'Ryan'
  ].every(i => obj.hasOwnProperty(i));
}