69 lines
1.2 KiB
Markdown
69 lines
1.2 KiB
Markdown
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---
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title: Iterate Through the Keys of an Object with a for...in Statement
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localeTitle: 使用for ... in Statement中的对象键迭代
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---
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## 使用for ... in Statement中的对象键迭代
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方法:
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* 注意: `dot-notation`会导致此挑战出错。
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* 必须使用`[square-bracket]`表示法来调用变量属性名称。
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* 以下代码无效。
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### 例1:
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```javascript
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for (let user in obj) {
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if(obj.user.online === true) {
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//code
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}
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}
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```
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* 示例2演示了如何使用`[square-bracket]`表示法执行代码。
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### 例2:
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```javascript
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for (let user in obj) {
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if(obj[user]online === true) {
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//code
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}
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}
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```
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### 解:
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```javascript
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let users = {
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Alan: {
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age: 27,
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online: false
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},
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Jeff: {
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age: 32,
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online: true
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},
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Sarah: {
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age: 48,
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online: false
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},
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Ryan: {
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age: 19,
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online: true
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}
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};
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function countOnline(obj) {
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// change code below this line
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let result = 0;
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for (let user in obj) {
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if(obj[user].online === true) {
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result++;
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}
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}
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return result;
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// change code above this line
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}
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console.log(countOnline(users));
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```
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