75 lines
1.8 KiB
Markdown
75 lines
1.8 KiB
Markdown
---
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title: With
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localeTitle: 同
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---
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## 同
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JavaScript的`with`语句是在一个对象上编辑多个属性的简便方法。大多数开发人员不鼓励使用`with` ，您最好不要使用此关键字。
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**注意** ： `"strict mode"`禁止使用`with` 。
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### 句法
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```syntax
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with (expression)
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statement
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```
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### 示例用法
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在JavaScript中，您可以单独修改对象的属性，如下所示：
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```javascript
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let earth = {};
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earth.moons = 1;
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earth.continents = 7;
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```
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`with`为您提供了修改对象属性的简写：
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```javascript
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with (earth) {
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moons = 1;
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continents = 7;
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}
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```
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虽然这个例子很做作，你能理解的用例`with`更多，如果你有更大的物体象下面这样：
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```javascript
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earth.continents.australia.geography.ocean = "Pacific";
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earth.continents.australia.geography.river = "Murray";
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earth.continents.australia.geography.mountain = "Kosciuszko";
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```
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### 备择方案
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你不应该使用它`with`因为它有微妙的错误和兼容性问题。强烈推荐的方法是将对象分配给变量，然后修改变量的属性。以下是使用更大对象的示例：
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```javascript
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let earth = {
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continents: {
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australia: {
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geography: {}
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}
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}
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};
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let geo = earth.continents.australia.geography;
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geo.ocean = "Pacific";
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geo.river = "Murray";
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geo.mountain = "Kosciuszko";
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```
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### 试试看
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https://repl.it/Mixg/5
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#### 更多信息：
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[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with)
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[https://yuiblog.com/blog/2006/04/11/with-statement-considered-harmful/](https://yuiblog.com/blog/2006/04/11/with-statement-considered-harmful/)
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[http://2ality.com/2011/06/with-statement.html](http://2ality.com/2011/06/with-statement.html) |