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Commit 5e45635

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Question 74
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‎README.md‎

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@@ -2948,9 +2948,9 @@ getYear();
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```
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- A: undefined - undefined - 2021
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- B: undefined - 2021 - 2021
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- C: 2021 - undefined - 2021
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- D: 2021 - 2021 - 2021
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- B: undefined - 2021 - 2021
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- C: 2021 - undefined - 2021
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- D: 2021 - 2021 - 2021
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<details><summary><b>Answer</b></summary>
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<p>
@@ -2967,3 +2967,67 @@ Be aware of the `setTimeout` method, which will create a separated context that
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</p>
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</details>
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###### 74. What's the output?
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```javascript
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class handleCovid {
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constructor(start) {
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this.start = start;
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}
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calculate(someValue) {
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this.start = this.start + someValue;
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return this.start;
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}
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vaccine() {
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++this.start;
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return this;
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}
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delaying() {
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++this.start;
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return this;
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}
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static getFinal(result) {
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return result * 2;
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}
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}
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const now = new handleCovid(2019);
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console.log(
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handleCovid.getFinal(now.vaccine().delaying().calculate(2020))
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);
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```
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- A: 2019
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- B: 8082
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- C: 8080
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- D: 8084
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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 code snippet above is ugly and sounds complicated at first. Yet, you might encounter a situation when some good "take away" messages might be given. The flow of the code is not hard to understand, I suppose.
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First, a function in JavaScript can accept another function as its parameter. With regard to the `static` keyword, it means we can directly call a static method in the form of `className.staticmethod` without invoking the object created by the normal way `new ClassName`.
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Besides, you might want to have a look at how we chain more than one method together. That is possible if these methods `return this`.
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Now let break it down:
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- `calculate(2020)` --> 2019 +たす 2020 =わ 4019;
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- `delaying().calculate(2020)` --> 4020;
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- `now.vaccine().delaying().calculate(2020)` --> 4021;
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- `handleCovid.getFinal(now.vaccine().delaying().calculate(2020)` --> 4021*2 = 8082;
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So the correct answer is B.
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</p>
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</details>

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