102 lines
1.5 KiB
Markdown
102 lines
1.5 KiB
Markdown
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---
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id: 56533eb9ac21ba0edf2244af
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title: 複合賦值之 +=
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/cDR6LCb'
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forumTopicId: 16661
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dashedName: compound-assignment-with-augmented-addition
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---
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# --description--
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在編程中，通常通過賦值來修改變量的內容。 記住，賦值時 JavaScript 會先計算等號右邊的內容，所以我們可以寫這樣的語句：
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```js
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myVar = myVar + 5;
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```
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給 `myVar` 加上 `5`。 這是最常見的運算賦值語句，即先運算、再賦值。還有一類操作符是一步到位，既做運算也賦值的。
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其中一種就是 `+=` 運算符。
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```js
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var myVar = 1;
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myVar += 5;
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console.log(myVar);
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```
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控制檯將會顯示 `6`。
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# --instructions--
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使用 `+=` 操作符對 `a`、`b` 和 `c` 賦值。
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# --hints--
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`a` 應該等於 `15`。
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```js
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assert(a === 15);
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```
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`b` 應該等於 `26`。
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```js
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assert(b === 26);
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```
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`c` 應該等於 `19`。
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```js
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assert(c === 19);
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```
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應該對每個變量使用 `+=` 操作符。
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```js
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assert(code.match(/\+=/g).length === 3);
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```
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不要修改註釋上面的代碼。
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```js
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assert(
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/var a = 3;/.test(code) &&
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/var b = 17;/.test(code) &&
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/var c = 12;/.test(code)
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);
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```
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# --seed--
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## --after-user-code--
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```js
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(function(a,b,c){ return "a = " + a + ", b = " + b + ", c = " + c; })(a,b,c);
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```
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## --seed-contents--
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```js
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var a = 3;
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var b = 17;
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var c = 12;
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// Only change code below this line
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a = a + 12;
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b = 9 + b;
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c = c + 7;
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```
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# --solutions--
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```js
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var a = 3;
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var b = 17;
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var c = 12;
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a += 12;
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b += 9;
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c += 7;
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```
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