Regex Conditional Lookahead JavaScript

Question

I just used regex101, to create the following regex.

([^,]*?)=(.*?)(?(?=, )(?:, )|(?:$))(?(?=[^,]*?=)(?:(?=[^,]*?=))|(?:$))

It seems to work perfectly for my use case of getting keys and values that are comma separated while still preserving commas in the values.

Problem is, I want to use this Regex in Node.js (JavaScript), but while writing this entire Regex in regex101, I had it set to PCRE (PHP).

It looks like JavaScript doesn't support Conditional Lookaheads ((?(?=...)()|()).

Is there a way to get this working in JavaScript?

Examples:

2 matches

group 1: id, group 2: 1

group 1: name, group 2: bob

id=1, name=bob

3 matches

group 1: id, group 2: 2

group 1: type, group 2: store

group 1: description, group 2: Hardwood Store

id=2, type=store, description=Hardwood Store

4 matches

group 1: id, group 2: 4

group 1: type, group 2: road

group 1: name, group 2: The longest road name, in the entire world, and universe, forever

group 1: built, group 2: 20190714

id=4, type=road, name=The longest road name, in the entire world, and universe, forever, built=20190714

3 matches

group 1: id, group 2: 3

group 1: type, group 2: building

group 1: builder, group 2: Random Name, and Other Person, with help from Final Person

id=3, type=building, builder=Random Name, and Other Person, with help from Final Person

Wiktor Stribiżew · Accepted Answer · 2019-07-14 20:48:26Z

1

You may use

/([^,=\s][^,=]*)=(.*?)(?=(?:,\s*)?[^,=]*=|$)/g

See the regex demo.

Details

([^,=\s][^,=]*) - Group 1:
- [^,=\s] - a char other than ,, = and whitespace
- [^,=]* - zero or more chars other than , and =
= - a = char
(.*?) - Group 2: any zero or more chars other than line break chars, as few as possible
(?=(?:,\s*)?[^,=]*=|$) - a positive lookahead that requires an optional sequence of , and 0+ whitespaces and then 0+ chars other than , and = and then a = or end of string immediately to the right of the current location

JS demo:

var strs = ['id=1, name=bob','id=2, type=store, description=Hardwood Store', 'id=4, type=road, name=The longest road name, in the entire world, and universe, forever, built=20190714','id=3, type=building, builder=Random Name, and Other Person, with help from Final Person']
var rx = /([^,=\s][^,=]*)=(.*?)(?=(?:,\s*)?[^,=]*=|$)/g;
for (var s of strs) {
   console.log("STRING:", s);
   var m;
   while (m=rx.exec(s)) {
     console.log(m[1], m[2])
   }
}

answered Jul 14, 2019 at 20:48

Wiktor Stribiżew

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2 Comments

Charlie Fish Over a year ago

This works really well! Thanks for the detailed explanation. Only problem, is I realized that some of the values have = signs in them as well. So now I have to figure out a way to ensure there is a comma before the =, or else it's part of the value. For example id=1, url=https://test.com/hello/world?name=bob, random=5. 3 matches here. id & 1, url & https://test.com/hello/world?name=bob, random & 5.

Wiktor Stribiżew Over a year ago

@CharlieFish I thought the comma and spaces are optional. If not use regex101.com/r/5fFQV5/3

Community · Accepted Answer · 2020-06-20 09:12:55Z

Maybe, these expressions would be somewhat close to what you might want to design:

([^=\n\r]*)=\s*([^=\n\r]*)\s*(?:,|$)

or

\s*([^=\n\r]*)=\s*([^=\n\r]*)\s*(?:,|$)

not sure though.

DEMO

The expression is explained on the top right panel of this demo if you wish to explore/simplify/modify it.

const regex = /\s*([^=\n\r]*)=\s*([^=\n\r]*)\s*(?:,|$)/gm;
const str = `id=3, type=building, builder=Random Name, and Other Person, with help from Final Person

id=4, type=road, name=The longest road name, in the entire world, and universe, forever, built=20190714

id=2, type=store, description=Hardwood Store
id=1, name=bob

`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

RegEx Circuit

jex.im visualizes regular expressions:

score 0 · Accepted Answer · 2019-07-15 21:12:01Z

Yet another way to do it

\s*([^,=]*?)\s*=\s*((?:(?![^,=]*=)[\S\s])*)(?=[=,]|$)

https://regex101.com/r/J6SSGr/1

Readable version

 \s* 
 ( [^,=]*? )                   # (1), Key
 \s* = \s*                     #       =
 (                             # (2 start), Value
      (?:
           (?! [^,=]* = )
           [\S\s] 
      )*
 )                             # (2 end)
 (?= [=,] | $ )

Ultimate PCRE version

\s*([^,=]*?)\s*=\s*((?:(?!\s*[^,=]*=)[\S\s])*(?<![,\s]))\s*(?=[=,\s]|$)

https://regex101.com/r/slfMR1/1

 \s*                           # Wsp trim
 ( [^,=]*? )                   # (1), Key
 \s* = \s*                     # Wsp trim =  Wsp trim
 (                             # (2 start), Value
      (?:
           (?! \s* [^,=]* = )
           [\S\s] 
      )*
      (?<! [,\s] )                  # Wsp trim
 )                             # (2 end)
 \s*                           # Wsp trim
 (?= [=,\s] | $ )              # Field seperator

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