freeCodeCamp/curriculum/challenges/espanol/02-javascript-algorithms-and-data-structures/basic-data-structures/iterate-through-the-keys-of-an-object-with-a-for...in-statement.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7b7d367417b2b2512b1d	Itera a través de las claves de un objeto con una sentencia "for...in"	1	301162	iterate-through-the-keys-of-an-object-with-a-for---in-statement

--description--

Sometimes you need to iterate through all the keys within an object. You can use a for...in loop to do this. The for...in loop looks like:

const refrigerator = {
  'milk': 1,
  'eggs': 12,
};

for (const food in refrigerator) {
  console.log(food, refrigerator[food]);
}

This code logs milk 1 and eggs 12, with each key-value pair on its own line.

We defined the variable food in the loop head and this variable was set to each of the object's keys on each iteration, resulting in each food's name being printed to the console.

NOTA: Los objetos no mantienen un orden para las claves almacenadas como lo hacen los arreglos; por lo tanto, la posición de una clave en un objeto, o el orden relativo en el que aparece, es irrelevante cuando se hace referencia o se accede a esa clave.

--instructions--

We've defined a function countOnline which accepts one argument, allUsers. Use a for...in statement inside this function to loop through the allUsers object and return the number of users whose online property is set to true. An example of an object which could be passed to countOnline is shown below. Each user will have an online property set to either true or false.

{
  Alan: {
    online: false
  },
  Jeff: {
    online: true
  },
  Sarah: {
    online: false
  }
}

--hints--

La función countOnline debe utilizar una sentencia for in para iterar por las claves del objeto que se le pasa.

assert(
  code.match(
    /for\s*\(\s*(var|let|const)\s+[a-zA-Z_$]\w*\s+in\s+[a-zA-Z_$]\w*\s*\)/
  )
);

La función countOnline debe devolver 1 cuando se le pasa el objeto { Alan: { online: false }, Jeff: { online: true }, Sarah: { online: false } }

assert(countOnline(usersObj1) === 1);

La función countOnline debe devolver 2 cuando se le pasa el objeto { Alan: { online: true }, Jeff: { online: false }, Sarah: { online: true } }

assert(countOnline(usersObj2) === 2);

La función countOnline debe devolver 0 cuando se le pasa el objeto { Alan: { online: false }, Jeff: { online: false }, Sarah: { online: false } }

assert(countOnline(usersObj3) === 0);

--seed--

--after-user-code--

const usersObj1 = {
  Alan: {
    online: false
  },
  Jeff: {
    online: true
  },
  Sarah: {
    online: false
  }
}

const usersObj2 = {
  Alan: {
    online: true
  },
  Jeff: {
    online: false
  },
  Sarah: {
    online: true
  }
}


const usersObj3 = {
  Alan: {
    online: false
  },
  Jeff: {
    online: false
  },
  Sarah: {
    online: false
  }
}

--seed-contents--

const users = {
  Alan: {
    online: false
  },
  Jeff: {
    online: true
  },
  Sarah: {
    online: false
  }
}

function countOnline(allUsers) {
  // Only change code below this line

  // Only change code above this line
}

console.log(countOnline(users));

--solutions--

function countOnline(allUsers) {
  let numOnline = 0;
  for(const user in allUsers){
    if(allUsers[user].online) {
      numOnline++;
    }
  }
  return numOnline;
}