Generate an Array of All Object Keys with Object.keys() doubt

JavaScript
1

I don’t know what wrong in this:

Your code so far


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

function getArrayOfUsers(obj) {
  // change code below this line
let arr=[...obj];
return arr.keys();
  // change code above this line
}

console.log(getArrayOfUsers(users));

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/basic-data-structures/generate-an-array-of-all-object-keys-with-object-keys

2

This line:

let arr = [...obj];

The ... syntax takes something that is iterable and basically goes through its values one by one. By putting in [] you are saying “take this iterable and convert it to an array”.

Iterable is something that you can iterate through, something with items in order, so an array-like thing. Arrays are iterable, so are strings (first character, second character, third character and so on).

Objects are not iterable: they have no order (edit: note that technically they do: integer keys in ascending order followed by string keys in insertion order, but they still aren’t iterables). This:

{ foo: 1, bar: 2}

Is effectively exactly the same as:

{ bar: 2, foo: 1}

So the let arr = [...obj] line doesn’t make sense, it’s a syntax error.

The Object.keys() function takes an object and returns all its keys in an array. Note that it’s written like that: it’s just a static function, Object.keys(someObjectYouWantTheKeysOf). So like:

> Object.keys({foo: 1, bar: 2})
['foo', 'bar']

Similarly, just for reference, there are two other similar functions:

> Object.values({foo: 1, bar: 2})
[1, 2]
> Object.entries({foo: 1, bar: 2})
[['foo', 1], ['bar', 2]]
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