CODEWITHSUNDEEP
javascriptregexparsinglookbehind
gui3
gui3

Reputation: 1877

regex lookbehind alternative for parser (js)

Good morning

(I saw this topic has a LOT of answers but I couldn't find one that fits)

I am writing a little parser in javascript that would cut the text into sections like this :

var tex = "hello   this :word is apart"

var parsed = [
  "hello",
  "   ",
  "this",
  " ",
  // ":word" should not be there, neither "word"
  " ",
  "is",
  "apart"
]

the perfect regex for this is :

/((?!:[a-z]+)([ ]+|(?<= |^)[a-z]*(?= |$)))/g

But it has a positive lookbehind that, as I read, was only implemented in javascript in 2018, so I guess many browser compatibility conflicts... and I would like it to have at least a little compatibility...

I considered :

Understand, I NEED words AND ALL spaces, and to exclude some words. I am open in other methods, like not using regex.

my last option :

removing the spaces-check and organising my whole regex in the right order, praying that ":word" would be kept in the "special words" group before anything else.

my question :

would that work in javascript, and be reliable ?

I tried 

/(((:[a-z]+)|([ ]+)|([a-z]*))/g

in https://regexr.com/ seems to work, will it work in every case ?

Upvotes: 0

Views: 81

Answers (2)

Poul Bak
Poul Bak

Reputation: 10930

I would use 2 regexes, first one matches the Words, you DON'T want and then replace them with an empty string, this is the simple regex:

/:\w+/g

Then replace with an empty string. Now you have a string, that can be parsed with this regex:

/([ ]+)|([a-z]*)/g

which is a simplified version of your second regex, since forbidden Words are already gone.

Upvotes: 1

AnonymousSB
AnonymousSB

Reputation: 3604

You said you're open to non-regex solutions, but I can give you one that includes both. Since you can't rely on lookbehind being supported, then just capture everything and filter out what you don't want, words followed by a colon.

const text = 'hello   this :word is apart';
const regex = /(\w+)|(:\w+)|(\s+)/g;
const parsed = text.match(regex).filter(word => !word.includes(':'));

console.log(parsed);

Upvotes: 1

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