62 lines
1.8 KiB
Markdown
62 lines
1.8 KiB
Markdown
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---
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title: New String Functions
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localeTitle: 新的字符串函数
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---
## 新的字符串函数
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以下四个函数在ES6中添加了新的字符串。
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* 以。。开始
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* 以。。结束
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* 包括
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* 重复
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## 以。。开始：
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这是一个区分大小写的函数，它可以帮助我们查找特定字符串是否以某个子字符串开头。
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startsWith接受名为position的第二个可选参数，当我们想要在搜索之前从字符串的开头跳过特定数量的字符时，我们可以使用它。
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```javascript
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const str ='Rachna';
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str.startsWith('Rad') //false
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str.startsWith('ra') //false as it is case sensitive
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str.startsWith('Ra') //true
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str.startsWith('ch',2) //true as we are searching from the second position
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str.startsWith('ch',3) //false
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```
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## 以。。结束
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这是一个区分大小写的函数，它可以帮助我们查找特定字符串是否以某个子字符串结尾。
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endsWith接受一个名为endPosition的第二个可选参数，我们可以使用它来包含搜索前的字符数。
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```javascript
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const city= 'Delhi';
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city.endsWith('Hi'); //false as it is case sensitive
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city.endsWith('hi');//true
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city.endsWith('l',3);//true - include only first three characters before searching
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city.endsWith('l',4);//false
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```
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## 包括
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includes函数也是一个区分大小写的函数，用于检查searchString是否存在于字符串中的任何位置。
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```javascript
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const name='John Doe';
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name.includes('do'); //false
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name.includes('D'); //true
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name.includes('Do'); //true
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```
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## 重复
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重复允许我们取一个字符串并重复多次。
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```javascript
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const str = 'This is repeated';
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str.repeat(3); //"This is repeatedThis is repeatedThis is repeated"
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```
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repeat函数可用于从左侧填充带有多个空格的字符串。
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