Question

我想匹配包含字符串yes的表达式，但前提是它前面没有字符串no。

例如，这与匹配： Hello world, major yes here!
但这不匹配：Hell no yes

第二个字符串不匹配，因为yes字符串前面有no字符串。显然，这需要否定的lookbehind，这在JavaScript正则表达式的味道中没有实现，我尝试过这样的东西： /((?!no ))yes/
/^(?!.*no) yes$/

但他们似乎没有达到预期的效果：/

Answer 1

您可以尝试下面的正则表达式。

^(?=(?:(?!\bno\b).)*yes).*

DEMO

<强>解释

^                        the beginning of the string
(?=                      look ahead to see if there is:
  (?:                      group, but do not capture (0 or more
                           times):
    (?!                      look ahead to see if there is not:
      \b                       the boundary between a word char
                               (\w) and something that is not a
                               word char
      no                       'no'
      \b                       the boundary between a word char
                               (\w) and something that is not a
                               word char
    )                        end of look-ahead
    .                        any character except \n
  )*                       end of grouping
  yes                      'yes'
)                        end of look-ahead
.*                       any character except \n (0 or more times)

Answer 2

我认为这里不需要正则表达式。你可以像这样做

var str = "Hell no yes", match = null, no = str.indexOf("no"), yes = str.indexOf("yes");
if(no >= 0 && (yes < 0 || no < yes)) { // check that no doesn't exist before yes
   match = str.match(/yes/)[0]; // then match the "yes"
}

Answer 3

这应该适合你：

var reg = /^((?!no).)*yes.*$/

console.log("Test some no and yes".match(reg))
console.log("Test some yes".match(reg))
console.log("Test some yes and no".match(reg))

请注意，它不适用于没有“是”字样的句子：

console.log("Test some without".match(reg))

以下是可能有助于解决问题的更多参考：

Regular expression to match string not containing a word?

在JavaScript中匹配一个单词而没有另一个单词的正则表达式

3 个答案: