Javascript RegExp构造函数属性输入
将全局标志设置为true:Javascript RegExp构造函数属性输入,javascript,regex,constructor,exec,Javascript,Regex,Constructor,Exec,将全局标志设置为true: <script> var str="I am really puzzled up"; var str1="Being puzzled is first step towards understanding"; var patt=new RegExp("puzzled","gi"); patt.exec(str); alert(RegExp.$_); //I am really puzzled up *[1] patt.exec(str1); alert
<script>
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
var patt=new RegExp("puzzled","gi");
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up *[1]
patt.exec(str1);
alert(RegExp.$_); //I am really puzzled up *[2]
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding *[3]
</script>
<script>
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
var patt=new RegExp("puzzled","i");
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding
</script>
var str=“我真的很困惑”;
var str1=“困惑是理解的第一步”;
var patt=新的RegExp(“困惑”、“gi”);
副执行官(str);
警报(RegExp.$)//我真的很困惑*[1]
副执行官(str1);
警报(RegExp.$)//我真的很困惑*[2]
副执行官(str1);
警报(RegExp.$)//困惑是理解的第一步*[3]
在不将全局标志设置为true的情况下:
<script>
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
var patt=new RegExp("puzzled","gi");
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up *[1]
patt.exec(str1);
alert(RegExp.$_); //I am really puzzled up *[2]
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding *[3]
</script>
<script>
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
var patt=new RegExp("puzzled","i");
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding
</script>
var str=“我真的很困惑”;
var str1=“困惑是理解的第一步”;
var patt=新的RegExp(“困惑的”、“i”);
副执行官(str);
警报(RegExp.$)//我真的很困惑
副执行官(str1);
警报(RegExp.$)//困惑是理解的第一步
已通过注释显示输出
- [1] -我对这一产出感到满意
- [2] -现在,当我已经将该模式与其他字符串构造函数匹配时,属性仍然显示第一个匹配的字符串
- [3] -只有再次将模式与字符串匹配,我才能获得所需的结果
patt.exec方法
两次才能更改“按构造函数更新结果”属性
问:只有当模式的global
标志设置为true
时,才会发生这种情况。如果未设置global标志,则第一次按构造函数属性更新结果。RegExp.exec如何工作?
当给定字符串时,RegExp.exec
将:
- 如果模式是全局模式(具有
标志),则它将在g
实例中使用RegExp
属性,并从指示的索引中搜索字符串以查找模式这意味着lastIndex
不知道输入字符串。它将只以索引为起点,搜索字符串,不管字符串是否与上一次调用相同 如果找到匹配项,它将返回一个带有匹配项的数组,并相应地更新RegExp.exec
实例中的字段,如中所示RegExp
将使用开始下一次匹配的位置进行更新 如果未找到匹配项,它将把lastIndex
重置为0,并在调用lastIndex
后返回RegExp.exec
null
var arr = pattern.exec(inputString);
if (arr !== null) {
// Print to the console the whole input string that has a match
console.log(arr.input);
}
g
未设置标志),lastIndex
属性将被忽略。无论lastIndex
属性如何,匹配始终从索引0开始
实例将存储开始下一次匹配的位置(RegExp
),标志的状态(lastIndex
,global
,multiline
)和模式的文本(ignorecase
)source
的返回值是存储匹配结果的数组。数组还具有存储输入字符串的RegExp.exec
属性和存储匹配项基于0的索引的input
属性index
RegExp
对象的RegExp.$\ucode>属性
RegExp.$\ucode>属性和RegExp
对象上的其他几个类似属性。只需通过RegExp.exec
返回的数组访问它们$\uu0
相当于RegExp.exec
返回的数组中附加的input
属性
var arr = pattern.exec(inputString);
if (arr !== null) {
// Print to the console the whole input string that has a match
console.log(arr.input);
}
由于这些属性位于RegExp
对象上,因此当您处理多个RegExp
实例时会非常混乱-您不知道这些属性是来自当前还是以前的执行,例如在本例中
从您得到的行为来看,RegExp.exec
找到匹配项时,RegExp.exec
似乎会修改,RegExp.exec
无法匹配时,不会修改它(上一个值保持不变)
对行为的解释
请阅读以上部分了解其工作原理的全貌
我在原始代码中添加了一些关于幕后发生的事情的注释:
全球标志
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
// Global pattern
var patt=new RegExp("puzzled","gi");
// From index 0 of str, found match at index 12
// RegExp.$_ is set to current input - str
// patt.lastIndex is set to index 19
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up *[1]
// From index 19 of str1, can't find any match
// Since no match is found, RegExp.$_'s value is not changed
// patt.lastIndex is set to 0
patt.exec(str1);
alert(RegExp.$_); //I am really puzzled up *[2]
// Found index 0 of str1, found match at index 6
// RegExp.$_ is set to current input - str1
// patt.lastIndex is set to 13
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding *[3]
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
// Not global
var patt=new RegExp("puzzled","i");
// From index 0 of str, found match at index 12
// RegExp.$_ is set to current input - str
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up
// From index 0 of str1, found match at index 6
// RegExp.$_ is set to current input - str1
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding
无全局标志
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
// Global pattern
var patt=new RegExp("puzzled","gi");
// From index 0 of str, found match at index 12
// RegExp.$_ is set to current input - str
// patt.lastIndex is set to index 19
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up *[1]
// From index 19 of str1, can't find any match
// Since no match is found, RegExp.$_'s value is not changed
// patt.lastIndex is set to 0
patt.exec(str1);
alert(RegExp.$_); //I am really puzzled up *[2]
// Found index 0 of str1, found match at index 6
// RegExp.$_ is set to current input - str1
// patt.lastIndex is set to 13
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding *[3]
var str="I am really puzzled up";
var str1="Being puzzled is first step towards understanding";
// Not global
var patt=new RegExp("puzzled","i");
// From index 0 of str, found match at index 12
// RegExp.$_ is set to current input - str
patt.exec(str);
alert(RegExp.$_); //I am really puzzled up
// From index 0 of str1, found match at index 6
// RegExp.$_ is set to current input - str1
patt.exec(str1);
alert(RegExp.$_); //Being puzzled is first step towards understanding
RegExp.exec
是如何工作的?
当给定字符串时,RegExp.exec
将:
- 如果模式是全局模式(具有
g
标志),则它将在RegExp
实例中使用lastIndex
属性,并从指示的索引中搜索字符串以查找模式这意味着RegExp.exec
不知道输入字符串。它将只以索引为起点,搜索字符串,不管字符串是否与上一次调用相同
如果找到匹配项,它将返回一个带有匹配项的数组,并相应地更新RegExp
实例中的字段,如中所示lastIndex
将使用开始下一次匹配的位置进行更新
如果未找到匹配项,它将把lastIndex
重置为0,并在调用RegExp.exec
后返回null
var arr = pattern.exec(inputString);
if (arr !== null) {
// Print to the console the whole input string that has a match
console.log(arr.input);
}
如果模式不是全局模式(g
未设置标志),lastIndex
属性将被忽略。无论lastIndex
属性如何,匹配始终从索引0开始
非常清楚地说:
RegExp
实例将存储开始下一次匹配的位置(lastIndex
),标志的状态(global
,multiline
,ignorecase
)和模式的文本(source
)
RegExp.exec
的返回值是存储匹配结果的数组。数组还具有input
属性,该属性存储输入字符串和