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id	title	challengeType	forumTopicId	dashedName
587d7b7d367417b2b2512b1c	Check if an Object has a Property	1	301155	check-if-an-object-has-a-property

--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.

--hints--

The users object should only contain the keys Alan, Jeff, Sarah, and Ryan

assert(
  'Alan' in users &&
    'Jeff' in users &&
    'Sarah' in users &&
    'Ryan' in users &&
    Object.keys(users).length === 4
);

The function isEveryoneHere should return true if Alan, Jeff, Sarah, and Ryan are properties on the users object

assert(isEveryoneHere(users) === true);

The function isEveryoneHere should return false if Alan is not a property on the users object

assert(
  (function () {
    delete users.Alan;
    return isEveryoneHere(users);
  })() === false
);

The function isEveryoneHere should return false if Jeff is not a property on the users object

assert(
  (function () {
    delete users.Jeff;
    return isEveryoneHere(users);
  })() === false
);

The function isEveryoneHere should return false if Sarah is not a property on the users object

assert(
  (function () {
    delete users.Sarah;
    return isEveryoneHere(users);
  })() === false
);

The function isEveryoneHere should return false if Ryan is not a property on the users object

assert(
  (function () {
    delete users.Ryan;
    return isEveryoneHere(users);
  })() === false
);

--seed--

--seed-contents--

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) {
  // Only change code below this line

  // Only change code above this line
}

console.log(isEveryoneHere(users));

--solutions--

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

console.log(isEveryoneHere(users));

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