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(?=) didn'work , i just change its position
The 2019 Stack Overflow Developer Survey Results Are InHow to change an element's class with JavaScript?How to validate an email address using a regular expression?How do you access the matched groups in a JavaScript regular expression?jQuery Set Cursor Position in Text Areaevent.preventDefault() vs. return falseHow to match “anything up until this sequence of characters” in a regular expression?What is the explanation for these bizarre JavaScript behaviours mentioned in the 'Wat' talk for CodeMash 2012?Regular expression search replace in Sublime Text 2Is Safari on iOS 6 caching $.ajax results?Python string.replace regular expression
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;
My regular expression did not execute correctly.
I get different results when I change its position.
"bbbWindows" is not what I wanted. Why not 'bbb2222'?
'Windowsbbb'.replace(/Windows(?=bbb)/, '2222') // 2222bbb
'bbbWindows'.replace(/(?=bbb)Windows/, '2222') // bbbWindows
javascript regex
asked Mar 22 at 2:53
Xu YoungXu Young
184
add a comment |
My regular expression did not execute correctly.
I get different results when I change its position.
"bbbWindows" is not what I wanted. Why not 'bbb2222'?
'Windowsbbb'.replace(/Windows(?=bbb)/, '2222') // 2222bbb
'bbbWindows'.replace(/(?=bbb)Windows/, '2222') // bbbWindows
javascript regex
asked Mar 22 at 2:53
Xu YoungXu Young
184
?= is a positive lookahead, and it captures nothing.
– Xhua
Mar 22 at 3:04
add a comment |
My regular expression did not execute correctly.
I get different results when I change its position.
"bbbWindows" is not what I wanted. Why not 'bbb2222'?
'Windowsbbb'.replace(/Windows(?=bbb)/, '2222') // 2222bbb
'bbbWindows'.replace(/(?=bbb)Windows/, '2222') // bbbWindows
javascript regex
asked Mar 22 at 2:53
Xu YoungXu Young
184
My regular expression did not execute correctly.
I get different results when I change its position.
"bbbWindows" is not what I wanted. Why not 'bbb2222'?
'Windowsbbb'.replace(/Windows(?=bbb)/, '2222') // 2222bbb
'bbbWindows'.replace(/(?=bbb)Windows/, '2222') // bbbWindows
javascript regex
javascript regex
asked Mar 22 at 2:53
Xu YoungXu Young
184
asked Mar 22 at 2:53
Xu YoungXu Young
184
asked Mar 22 at 2:53
Xu YoungXu Young
184
asked Mar 22 at 2:53
Xu YoungXu Young
184
asked Mar 22 at 2:53
Xu YoungXu Young
184
184
?= is a positive lookahead, and it captures nothing.
– Xhua
Mar 22 at 3:04
add a comment |
?= is a positive lookahead, and it captures nothing.
– Xhua
Mar 22 at 3:04
?= is a positive lookahead, and it captures nothing.
– Xhua
Mar 22 at 3:04
?= is a positive lookahead, and it captures nothing.
– Xhua
Mar 22 at 3:04
add a comment |
2 Answers
2
active
oldest
votes
Lookaheads ((?=...)) are zero-length assertions. They assert that the substring following that position in the original string must match the given pattern. In other words,
/Windows(?=bbb)/
Will match the substring Windows only if the substring immediately following the s also matches the pattern bbb. On the other hand,
/(?=bbb)Windows/
Will match the substring Windows only if the substring immediately following start position of the initial match also matches the pattern bbb—which is impossible, no string will ever match that.
The easiest way to get this pattern to work would be to use a regular 'in-line' group ((...)) and tweak your replacement string to insert this matched substring in the appropriate place ($N). For example:
console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
add a comment |
You should use positive lookbehind when the asserted pattern is behind the matching pattern:
'bbbWindows'.replace(/(?<=bbb)Windows/, '2222')
answered Mar 22 at 2:57
blhsingblhsing
43k41743
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
add a comment |
Your Answer
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Lookaheads ((?=...)) are zero-length assertions. They assert that the substring following that position in the original string must match the given pattern. In other words,
/Windows(?=bbb)/
Will match the substring Windows only if the substring immediately following the s also matches the pattern bbb. On the other hand,
/(?=bbb)Windows/
Will match the substring Windows only if the substring immediately following start position of the initial match also matches the pattern bbb—which is impossible, no string will ever match that.
The easiest way to get this pattern to work would be to use a regular 'in-line' group ((...)) and tweak your replacement string to insert this matched substring in the appropriate place ($N). For example:
console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
add a comment |
Lookaheads ((?=...)) are zero-length assertions. They assert that the substring following that position in the original string must match the given pattern. In other words,
/Windows(?=bbb)/
Will match the substring Windows only if the substring immediately following the s also matches the pattern bbb. On the other hand,
/(?=bbb)Windows/
Will match the substring Windows only if the substring immediately following start position of the initial match also matches the pattern bbb—which is impossible, no string will ever match that.
The easiest way to get this pattern to work would be to use a regular 'in-line' group ((...)) and tweak your replacement string to insert this matched substring in the appropriate place ($N). For example:
console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
add a comment |
Lookaheads ((?=...)) are zero-length assertions. They assert that the substring following that position in the original string must match the given pattern. In other words,
/Windows(?=bbb)/
Will match the substring Windows only if the substring immediately following the s also matches the pattern bbb. On the other hand,
/(?=bbb)Windows/
Will match the substring Windows only if the substring immediately following start position of the initial match also matches the pattern bbb—which is impossible, no string will ever match that.
The easiest way to get this pattern to work would be to use a regular 'in-line' group ((...)) and tweak your replacement string to insert this matched substring in the appropriate place ($N). For example:
console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
Lookaheads ((?=...)) are zero-length assertions. They assert that the substring following that position in the original string must match the given pattern. In other words,
/Windows(?=bbb)/
Will match the substring Windows only if the substring immediately following the s also matches the pattern bbb. On the other hand,
/(?=bbb)Windows/
Will match the substring Windows only if the substring immediately following start position of the initial match also matches the pattern bbb—which is impossible, no string will ever match that.
The easiest way to get this pattern to work would be to use a regular 'in-line' group ((...)) and tweak your replacement string to insert this matched substring in the appropriate place ($N). For example:
console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222console.log('Windowsbbb'.replace(/Windows(bbb)/, '2222$1')) // 2222bbb
console.log('bbbWindows'.replace(/(bbb)Windows/, '$12222')) // bbb2222answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
edited Mar 22 at 3:38
answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
answered Mar 22 at 3:27
p.s.w.gp.s.w.g
120k19216257
120k19216257
add a comment |
add a comment |
You should use positive lookbehind when the asserted pattern is behind the matching pattern:
'bbbWindows'.replace(/(?<=bbb)Windows/, '2222')
answered Mar 22 at 2:57
blhsingblhsing
43k41743
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
add a comment |
You should use positive lookbehind when the asserted pattern is behind the matching pattern:
'bbbWindows'.replace(/(?<=bbb)Windows/, '2222')
answered Mar 22 at 2:57
blhsingblhsing
43k41743
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
add a comment |
You should use positive lookbehind when the asserted pattern is behind the matching pattern:
'bbbWindows'.replace(/(?<=bbb)Windows/, '2222')
answered Mar 22 at 2:57
blhsingblhsing
43k41743
You should use positive lookbehind when the asserted pattern is behind the matching pattern:
'bbbWindows'.replace(/(?<=bbb)Windows/, '2222')
answered Mar 22 at 2:57
blhsingblhsing
43k41743
answered Mar 22 at 2:57
blhsingblhsing
43k41743
answered Mar 22 at 2:57
blhsingblhsing
43k41743
answered Mar 22 at 2:57
blhsingblhsing
43k41743
43k41743
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
add a comment |
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
Lookbehinds are not supported in JavaScript.
– p.s.w.g
Mar 22 at 3:17
add a comment |
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?= is a positive lookahead, and it captures nothing.
– Xhua
Mar 22 at 3:04