What's the output?

Question

```javascript
const getList = ([x, ...y]) => [x, y]
const getUser = user => { name: user.name, age: user.age }

const list = [1, 2, 3, 4]
const user = { name: "Lydia", age: 21 }

console.log(getList(list))
console.log(getUser(user))
```

Accepted Answer

The `getList` function receives an array as its argument. Between the parentheses of the `getList` function, we destructure this array right away. You could see this as:

`[x, ...y] = [1, 2, 3, 4]`

With the rest parameter `...y`, we put all "remaining" arguments in an array. The remaining arguments are `2`, `3` and `4` in this case. The value of `y` is an array, containing all the rest parameters. The value of `x` is equal to `1` in this case, so when we log `[x, y]`, `[1, [2, 3, 4]]` gets logged.

The `getUser` function receives an object. With arrow functions, we don't _have_ to write curly brackets if we just return one value. However, if you want to instantly return an _object_ from an arrow function, you have to write it between parentheses, otherwise everything between the two braces will be interpreted as a block statement. In this case the code between the braces is not a valid JavaScript code, so a `SyntaxError` gets thrown.

The following function would have returned an object:

`const getUser = user => ({ name: user.name, age: user.age })`

Conceitos relacionados

What's the output?

What does this method do?

Qual o resultado?

Conceitos relacionados

Conceitos relacionados

What's the output?

What does this method do?

Qual o resultado?

Conceitos relacionados