JavasScript RegEx Replace Pattern in String that Looks Like An Array

Question

I have an array in string-format. With Javascript, how to replace [, ], <Tag: , and > in the least amount of code possible:

let s = "[<Tag: cats>, <Tag: dogs>, <Tag: parakeets>]"

End result should look like:

"cats, dogs, parakeets"

This seems to work, but it's pretty... not great.

s.replace(/^\[/, '').replace(/\]$/, '').replaceAll('<Tag: ', '').replaceAll('>', '')

Is there a clever way to do this with RegEx?

CertainPerformance · Accepted Answer · 2021-10-22 20:25:17Z

2

Matching <Tag: and then capturing non-> characters looks like it'd do what you want:

const s = "[<Tag: cats>, <Tag: dogs>, <Tag: parakeets>]";
const result = s.replace(/<Tag: ([^>]+)>/g, '$1').replace(/[[\]]/g, '');
console.log(result);

Another approach, matching instead of replacing:

const s = "[<Tag: cats>, <Tag: dogs>, <Tag: parakeets>]";
const result = [...s.matchAll(/<Tag: ([^>]+)>/g)]
  .map(match => match[1])
  .join(', ');
console.log(result);

answered Oct 22, 2021 at 20:25

CertainPerformance

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3 Comments

Robo Robok Over a year ago

How about using (.+?) instead of ([^>]+)?

CertainPerformance Over a year ago

Lazy repetition, while it looks nicer, is less efficient than a negative character set

Robo Robok Over a year ago

I just ran a benchmark: html.matchAll(/<[^>]+>/g) vs. html.matchAll(/<.+?>/g) on this page's HTML source code and the latter one was faster by 6.5%.

Robo Robok · Accepted Answer · 2021-10-22 20:26:55Z

2

I would suggest matching all substrings and joining them:

const result = [...s.matchAll(/<Tag:\s*(\w+)>/g)]
    .map(
        ([, m]) => m
    )
    .join(', ');


// result: "cats, dogs, parakeets"

answered Oct 22, 2021 at 20:26

Robo Robok

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2 Comments

Jarad Over a year ago

Slight issue. If tag is multi-word (ex: <Tag: something with spaces>) the regex needs to allow for spaces. I failed to provide an example in my initial question. I think ([\w\s]+) will work.

Robo Robok Over a year ago

@Jarad yes, if you need spaces then what you suggested will work :)

The fourth bird · Accepted Answer · 2021-10-22 20:51:38Z

1

When an infinite quantifier in a lookbehind is supported, you can match all the values between <Tag: and the > and make sure all the matches are between square brackets.

See the regex matches in this regex demo.

let s = "[<Tag: cats>, <Tag: dogs>, <Tag: parakeets>]"
const regex = /(?<=\[[^\][]*<Tag: )\w+(?=>[^\][]*\])/g;
console.log(s.match(regex).join(", "));

answered Oct 22, 2021 at 20:51

The fourth bird

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Comments

trincot · Accepted Answer · 2021-10-22 20:29:41Z

0

What about this? Remove the delimiters [, ], > and <Tag: parts:

let s = "[<Tag: cats>, <Tag: dogs>, <Tag: parakeets>]";
s = s.replace(/[[\]>]|<.*? /g, "");
console.log(s);

answered Oct 22, 2021 at 20:29

trincot

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6 Comments

Jarad Over a year ago

FYI: I didn't downvote. Your answer seems to work on my simple string. I too would like to know what might be wrong with your answer. It is probably the shortest.

Robo Robok Over a year ago

I didn't downvote neither, but even though your answer will work in this case, when designing a pattern for regex, you should avoid false positives. It's just not the greatest pattern, may lead to unstable results.

ASDFGerte Over a year ago

Not my downvote, but there is imho no reason to use "<.*? " instead of "<Tag: ". This disallows spaces and brackets in the text, uses a ".*?" (which should be considerably more work than necessary, albeit this difference usually being irrelevant), and is harder to read and grasp the intention from, at least imho.

trincot Over a year ago

Some other answers create intermediate arrays... or perform two replace calls, and they get upvoted. I'm lost.

Robo Robok Over a year ago

@trincot but they are more readable than yours.

|

Anshu Jain · Accepted Answer · 2021-10-22 20:39:54Z

0

Not using a regex but it does return the same result that need.

let res = ""
let s = "[<Tag: cats>, <Tag: dogs>, <Tag: parakeets>]"

for ( let i = 0; i < s.length; i++){
  let c = s[i]
  if ( c == '[' || c == ']' || c == '>')
    continue
  else if ( s.substr(i,5) == '<Tag:')
    i += 5
  else
    res += c
}
return res

answered Oct 22, 2021 at 20:39

Anshu Jain

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