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字符串的使用方法之startwith()-以XX开头、endsWith()-以XX结尾、trim()-删除两端空格
2022-07-06 12:51:00 【viceen】
字符串的使用方法之startwith()-以XX开头、endsWith()-以XX结尾、trim()-删除两端空格
1、startsWith()方法
- 用来判断字符串是否以固定数据开头。
'abc'.startsWith('a') //true
'abc'.startsWith('d') //false
- 该方法还有第二个参数,可以从字符串指定位置开始判断,默认为0
'abcdefg'.startsWith('bcd')) //false
'abcdefg'.startsWith('bcd',1)) //true
2、endsWith()方法
- 第二个参数为所选字符串指定长度
'abc'.endsWith('c') //true
'abc'.endsWith('bc') //true
'abc'.endsWith('a') //false
'abcdefg'.endsWith('def')) //false
'abcdefg'.endsWith('def',6)) //true
3、trim()方法
- 从原始字符串的开头和结尾删除空格,中间的空格不进行处理。
- 并不影响原字符串本身,返回一个新字符串。
'Testing'.trim() //'Testing'
' Testing'.trim() //'Testing'
' Testing '.trim() //'Testing'
'Testing '.trim() //'Testing'
实例
<script>
var str = " yang ";
console.log(str);//输出 yang
var str1 = str.trim();//有返回值,要一个值接受
console.log(str1);//输出yang (没有空格)
var str2 = "ya ng";
console.log(str2);//输出"ya ng"
var str3 = str2.trim();
//从一个字符串的**两端**删除空白字符。字符串中间的空格不会删除
console.log(str3);//输出"ya ng"
</script>
使用正则表达式实现字符串的trim方法
String.prototype._trim = function() {
return this.replace(/^(\s*)|(\s*)$/g, '')
}
var str = ' ssss '
console.log(str) // 同上
console.log(str.length) // 11
var strNew = str._trim()
console.log(strNew) // 'ssss'
console.log(strNew.length) // 4
- 这里的*表示匹配0个或者多个,
- 此时我们需要考虑两种情况,一个是前面存在空格,另一个是后面存在空格。所以我们使用
|
来进行匹配。 - 并且使用
replace
来进行替换的话,只会替换第一个,所以我们需要加上全局匹配g
。
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