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Merge pull request lydiahallie#359 from lydiahallie/new
Add questions 146-150
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‎README.md‎

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</p>
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</details>
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---
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###### 146. What's the output?
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```javascript
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let count = 0;
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const nums = [0, 1, 2, 3];
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nums.forEach(num => {
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if (num) count += 1
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})
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console.log(count)
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```
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- A: 1
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- B: 2
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- C: 3
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- D: 4
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: C
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The `if` condition within the `forEach` loop checks whether the value of `num` is truthy or falsy. Since the first number in the `nums` array is `0`, a falsy value, the `if` statement's code block won't be executed. `count` only gets incremented for the other 3 numbers in the `nums` array, `1`, `2` and `3`. Since `count` gets incremented by `1` 3 times, the value of `count` is `3`.
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</p>
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</details>
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---
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###### 147. What's the output?
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```javascript
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function getFruit(fruits) {
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console.log(fruits?.[1]?.[1])
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}
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getFruit([['🍊', '🍌'], ['🍍']])
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getFruit()
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getFruit([['🍍'], ['🍊', '🍌']])
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```
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- A: `null`, `undefined`, 🍌
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- B: `[]`, `null`, 🍌
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- C: `[]`, `[]`, 🍌
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- D: `undefined`, `undefined`, 🍌
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: D
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The `?` allows us to optionally access deeper nested properties within objects. We're trying to log the item on index `1` within the subarray that's on index `1` of the `fruits` array. If the subarray on index `1` in the `fruits` array doesn't exist, it'll simply return `undefined`. If the subarray on index `1` in the `fruits` array exists, but this subarray doesn't have an item on its `1` index, it'll also return `undefined`.
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First, we're trying to log the second item in the `['🍍']` subarray of `[['🍊', '🍌'], ['🍍']]]`. This subarray only contains one item, which means there is no item on index `1`, and returns `undefined`.
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Then, we're invoking the `getFruits` function without passing a value as an argument, which means that `fruits` has a value of `undefined` by default. Since we're conditionally chaining the item on index `1` of`fruits`, it returns `undefined` since this item on index `1` does not exist.
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Lastly, we're trying to log the second item in the `['🍊', '🍌']` subarray of `['🍍'], ['🍊', '🍌']`. The item on index `1` within this subarray is `🍌`, which gets logged.
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</p>
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</details>
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---
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###### 148. What's the output?
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```javascript
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class Calc {
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constructor() {
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this.count = 0
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}
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increase() {
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this.count ++
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}
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}
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const calc = new Calc()
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new Calc().increase()
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console.log(calc.count)
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```
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- A: `0`
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- B: `1`
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- C: `undefined`
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- D: `ReferenceError`
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: A
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We set the variable `calc` equal to a new instance of the `Calc` class. Then, we instantiate a new instance of `Calc`, and invoke the `increase` method on this instance. Since the count property is within the constructor of the `Calc` class, the count property is not shared on the prototype of `Calc`. This means that the value of count has not been updated for the instance calc points to, count is still `0`.
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</p>
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</details>
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---
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###### 149. What's the output?
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```javascript
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const user = {
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email: "[email protected]",
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password: "12345"
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}
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const updateUser = ({ email, password }) => {
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if (email) {
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Object.assign(user, { email })
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}
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if (password) {
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user.password = password
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}
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return user
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}
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const updatedUser = updateUser({ email: "[email protected]" })
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console.log(updatedUser === user)
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```
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- A: `false`
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- B: `true`
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- C: `TypeError`
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- D: `ReferenceError`
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: B
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The `updateUser` function updates the values of the `email` and `password` properties on user, if their values are passed to the function, after which the function returns the `user` object. The returned value of the `updateUser` function is the `user` object, which means that the value of updatedUser is a reference to the same `user` object that `user` points to. `updatedUser === user` equals `true`.
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</p>
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</details>
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---
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###### 150. What's the output?
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```javascript
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const fruit = ['🍌', '🍊', '🍎']
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fruit.slice(0, 1)
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fruit.splice(0, 1)
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fruit.unshift('🍇')
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```
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- A: `['🍌', '🍊', '🍎']`
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- B: `['🍊', '🍎']`
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- C: `['🍇', '🍊', '🍎']`
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- D: `['🍇', '🍌', '🍊', '🍎']`
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: C
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First, we invoke the `slice` method on the fruit array. The slice method does not modify the original array, but returns the value that it sliced off the array: the banana emoji.
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Then, we invoke the `splice` method on the fruit array. The splice method does modify the original array, which means that the fruit array now consists of `['🍊', '🍎']`.
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At last, we invoke the `unshift` method on the `fruit` array, which modifies the original array by adding the provided value, ‘🍇’ in this case, as the first element in the array. The fruit array now consists of `['🍇', '🍊', '🍎']`.
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</p>
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</details>

‎en-EN/README.md‎

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</p>
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</details>
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-----
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###### 146. What's the output?
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```javascript
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let count = 0;
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const nums = [0, 1, 2, 3];
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nums.forEach(num => {
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if (num) count += 1
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})
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console.log(count)
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```
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- A: 1
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- B: 2
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- C: 3
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- D: 4
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: C
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The `if` condition within the `forEach` loop checks whether the value of `num` is truthy or falsy. Since the first number in the `nums` array is `0`, a falsy value, the `if` statement's code block won't be executed. `count` only gets incremented for the other 3 numbers in the `nums` array, `1`, `2` and `3`. Since `count` gets incremented by `1` 3 times, the value of `count` is `3`.
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</p>
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</details>
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---
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###### 147. What's the output?
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```javascript
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function getFruit(fruits) {
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console.log(fruits?.[1]?.[1])
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}
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getFruit([['🍊', '🍌'], ['🍍']])
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getFruit()
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getFruit([['🍍'], ['🍊', '🍌']])
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```
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- A: `null`, `undefined`, 🍌
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- B: `[]`, `null`, 🍌
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- C: `[]`, `[]`, 🍌
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- D: `undefined`, `undefined`, 🍌
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: D
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The `?` allows us to optionally access deeper nested properties within objects. We're trying to log the item on index `1` within the subarray that's on index `1` of the `fruits` array. If the subarray on index `1` in the `fruits` array doesn't exist, it'll simply return `undefined`. If the subarray on index `1` in the `fruits` array exists, but this subarray doesn't have an item on its `1` index, it'll also return `undefined`.
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First, we're trying to log the second item in the `['🍍']` subarray of `[['🍊', '🍌'], ['🍍']]]`. This subarray only contains one item, which means there is no item on index `1`, and returns `undefined`.
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Then, we're invoking the `getFruits` function without passing a value as an argument, which means that `fruits` has a value of `undefined` by default. Since we're conditionally chaining the item on index `1` of`fruits`, it returns `undefined` since this item on index `1` does not exist.
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Lastly, we're trying to log the second item in the `['🍊', '🍌']` subarray of `['🍍'], ['🍊', '🍌']`. The item on index `1` within this subarray is `🍌`, which gets logged.
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</p>
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</details>
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---
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###### 148. What's the output?
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```javascript
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class Calc {
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constructor() {
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this.count = 0
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}
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increase() {
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this.count ++
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}
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}
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const calc = new Calc()
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new Calc().increase()
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console.log(calc.count)
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```
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- A: `0`
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- B: `1`
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- C: `undefined`
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- D: `ReferenceError`
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: A
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We set the variable `calc` equal to a new instance of the `Calc` class. Then, we instantiate a new instance of `Calc`, and invoke the `increase` method on this instance. Since the count property is within the constructor of the `Calc` class, the count property is not shared on the prototype of `Calc`. This means that the value of count has not been updated for the instance calc points to, count is still `0`.
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</p>
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</details>
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---
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###### 149. What's the output?
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```javascript
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const user = {
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email: "[email protected]",
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password: "12345"
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}
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const updateUser = ({ email, password }) => {
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if (email) {
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Object.assign(user, { email })
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}
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if (password) {
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user.password = password
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}
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return user
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}
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const updatedUser = updateUser({ email: "[email protected]" })
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console.log(updatedUser === user)
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```
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- A: `false`
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- B: `true`
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- C: `TypeError`
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- D: `ReferenceError`
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: B
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The `updateUser` function updates the values of the `email` and `password` properties on user, if their values are passed to the function, after which the function returns the `user` object. The returned value of the `updateUser` function is the `user` object, which means that the value of updatedUser is a reference to the same `user` object that `user` points to. `updatedUser === user` equals `true`.
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</p>
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</details>
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---
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###### 150. What's the output?
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```javascript
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const fruit = ['🍌', '🍊', '🍎']
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fruit.slice(0, 1)
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fruit.splice(0, 1)
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fruit.unshift('🍇')
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```
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- A: `['🍌', '🍊', '🍎']`
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- B: `['🍊', '🍎']`
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- C: `['🍇', '🍊', '🍎']`
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- D: `['🍇', '🍌', '🍊', '🍎']`
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<details><summary><b>Answer</b></summary>
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<p>
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#### Answer: C
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First, we invoke the `slice` method on the fruit array. The slice method does not modify the original array, but returns the value that it sliced off the array: the banana emoji.
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Then, we invoke the `splice` method on the fruit array. The splice method does modify the original array, which means that the fruit array now consists of `['🍊', '🍎']`.
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At last, we invoke the `unshift` method on the `fruit` array, which modifies the original array by adding the provided value, ‘🍇’ in this case, as the first element in the array. The fruit array now consists of `['🍇', '🍊', '🍎']`.
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</p>
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</details>

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