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Add questions 151 - 153
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‎README.md

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<span>I post multiple choice JavaScript questions on my [Instagram](https://www.instagram.com/theavocoder) **stories**, which I'll also post here! Last updated: <a href=#20191224><b>December 24th</b></a>
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<span>I post multiple choice JavaScript questions on my [Instagram](https://www.instagram.com/theavocoder) **stories**, which I'll also post here! Last updated: <a href=#20200608><b>June 8th</b></a>
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From basic to advanced: test how well you know JavaScript, refresh your knowledge a bit, or prepare for your coding interview! :muscle: :rocket: I update this repo regularly with new questions. I added the answers in the **collapsed sections** below the questions, simply click on them to expand it. It's just for fun, good luck! :heart:</span>
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</p>
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</details>
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---
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###### <a name=20200608></a>151. What's the output?
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```javascript
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const animals = {};
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let dog = { emoji: '🐶' }
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let cat = { emoji: '🐈' }
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animals[dog] = { ...dog, name: "Mara" }
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animals[cat] = { ...cat, name: "Sara" }
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console.log(animals[dog])
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```
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- A: `{ emoji: "🐶", name: "Mara" }`
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- B: `{ emoji: "🐈", name: "Sara" }`
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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: B
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Object keys are converted to strings.
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Since the value of `dog` is an object, `animals[dog]` actually means that we’re creating a new property called `"object Object"` equal to the new object. `animals["object Object"]` is now equal to `{ emoji: "🐶", name: "Mara"}`.
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`cat` is also an object, which means that `animals[cat]` actually means that we’re overwriting the value of `animals[``"``object Object``"``]` with the new cat properties.
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Logging `animals[dog]`, or actually `animals["object Object"]` since converting the `dog` object to a string results `"object Object"`, returns the `{ emoji: "🐈", name: "Sara" }`.
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</p>
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</details>
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---
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###### 152. 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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updateEmail: email => {
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this.email = email
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}
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}
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user.updateEmail("[email protected]")
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console.log(user.email)
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```
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- A: `my@email.com`
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- B: `new@email.com`
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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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The `updateEmail` function is an arrow function, and is not bound to the `user` object. This means that the `this` keyword is not referring to the `user` object, but refers to the global scope in this case. The value of `email` within the `user` object does not get updated. When logging the value of `user.email`, the original value of `my@email.com` gets returned.
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</p>
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</details>
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---
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###### 153. What's the output?
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```javascript
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const promise1 = Promise.resolve('First')
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const promise2 = Promise.resolve('Second')
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const promise3 = Promise.reject('Third')
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const promise4 = Promise.resolve('Fourth')
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const runPromises = async () => {
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const res1 = await Promise.all([promise1, promise2])
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const res2 = await Promise.all([promise3, promise4])
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return [res1, res2]
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}
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runPromises()
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.then(res => console.log(res))
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.catch(err => console.log(err))
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```
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- A: `[['First', 'Second'], ['Fourth']]`
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- B: `[['First', 'Second'], ['Third', 'Fourth']]`
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- C: `[['First', 'Second']]`
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- D: `'Third'`
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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 `Promise.all` method runs the passed promises in parallel. If one promise fails, the `Promise.all` method _rejects) with the value of the rejected promise. In this case, `promise3` rejected with the value `"Third"`. We’re catching the rejected value in the chained `catch` method on the `runPromises` invocation to catch any errors within the `runPromises` function. Only `"Third"` gets logged, since `promise3` rejected with this value.
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</p>
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</details>

‎en-EN/README.md

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7-
<span>I post multiple choice JavaScript questions on my [Instagram](https://www.instagram.com/theavocoder) **stories**, which I'll also post here! Last updated: <a href=#20191224><b>December 24th</b></a>
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<span>I post multiple choice JavaScript questions on my [Instagram](https://www.instagram.com/theavocoder) **stories**, which I'll also post here! Last updated: <a href=#20200608><b>June 8th</b></a>
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99
From basic to advanced: test how well you know JavaScript, refresh your knowledge a bit, or prepare for your coding interview! :muscle: :rocket: I update this repo regularly with new questions. I added the answers in the **collapsed sections** below the questions, simply click on them to expand it. It's just for fun, good luck! :heart:</span>
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@@ -4886,3 +4886,106 @@ At last, we invoke the `unshift` method on the `fruit` array, which modifies the
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</p>
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</details>
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---
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###### <a name=20200608></a>151. What's the output?
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```javascript
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const animals = {};
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let dog = { emoji: '🐶' }
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let cat = { emoji: '🐈' }
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animals[dog] = { ...dog, name: "Mara" }
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animals[cat] = { ...cat, name: "Sara" }
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console.log(animals[dog])
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```
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- A: `{ emoji: "🐶", name: "Mara" }`
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- B: `{ emoji: "🐈", name: "Sara" }`
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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: B
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Object keys are converted to strings.
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Since the value of `dog` is an object, `animals[dog]` actually means that we’re creating a new property called `"object Object"` equal to the new object. `animals["object Object"]` is now equal to `{ emoji: "🐶", name: "Mara"}`.
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`cat` is also an object, which means that `animals[cat]` actually means that we’re overwriting the value of `animals[``"``object Object``"``]` with the new cat properties.
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Logging `animals[dog]`, or actually `animals["object Object"]` since converting the `dog` object to a string results `"object Object"`, returns the `{ emoji: "🐈", name: "Sara" }`.
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</p>
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</details>
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---
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###### 152. 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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updateEmail: email => {
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this.email = email
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}
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}
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user.updateEmail("[email protected]")
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console.log(user.email)
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```
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- A: `my@email.com`
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- B: `new@email.com`
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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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The `updateEmail` function is an arrow function, and is not bound to the `user` object. This means that the `this` keyword is not referring to the `user` object, but refers to the global scope in this case. The value of `email` within the `user` object does not get updated. When logging the value of `user.email`, the original value of `my@email.com` gets returned.
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</p>
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</details>
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---
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###### 153. What's the output?
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```javascript
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const promise1 = Promise.resolve('First')
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const promise2 = Promise.resolve('Second')
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const promise3 = Promise.reject('Third')
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const promise4 = Promise.resolve('Fourth')
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const runPromises = async () => {
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const res1 = await Promise.all([promise1, promise2])
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const res2 = await Promise.all([promise3, promise4])
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return [res1, res2]
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}
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runPromises()
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.then(res => console.log(res))
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.catch(err => console.log(err))
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```
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- A: `[['First', 'Second'], ['Fourth']]`
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- B: `[['First', 'Second'], ['Third', 'Fourth']]`
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- C: `[['First', 'Second']]`
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- D: `'Third'`
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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 `Promise.all` method runs the passed promises in parallel. If one promise fails, the `Promise.all` method _rejects) with the value of the rejected promise. In this case, `promise3` rejected with the value `"Third"`. We’re catching the rejected value in the chained `catch` method on the `runPromises` invocation to catch any errors within the `runPromises` function. Only `"Third"` gets logged, since `promise3` rejected with this value.
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</p>
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</details>

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