Why is /.+\[[0-9]+\]/g not correctly splitting "hello[0][1][3]"

Question

So I have this regex: /.+\[[0-9]+\]/g
and this string hello[0][1][3]

And I am trying to split that into - hello[0], hello[0][1] and hello[0][1][3] using regex.exec(...) but I am getting hello[0][1][3] as the only match.

How can I modify the regular expression to get the desired result

The regex in the question title is significantly different from the regex in the question text. Which is it? — Pointy, Aug 13 '20 at 12:13
.. because of how the regex starts ... `.+` is greedy and already does match any string entirely. — Peter Seliger, Aug 13 '20 at 12:15
Does this answer your question? [What do 'lazy' and 'greedy' mean in the context of regular expressions?](https://stackoverflow.com/questions/2301285/what-do-lazy-and-greedy-mean-in-the-context-of-regular-expressions) — luk2302, Aug 13 '20 at 12:16
btw ... what is the desired output/result supposed to look like? — Peter Seliger, Aug 13 '20 at 12:17
@luk2302 What change do you suggest I make to get the desired result? — Tony, Aug 13 '20 at 12:19
[Here](https://regex101.com/r/AL4Fyt/1) is a way to go. Caution: it will work for 3 groups only! — Toto, Aug 13 '20 at 12:26
@Toto I need to capture any number of groups, I only used 3 as an example — Tony, Aug 13 '20 at 12:43
A regex can only match distinct substrings. You cannot have one regex that will produce matches which are overlapping. — trincot, Aug 13 '20 at 21:47

score 0 · Answer 1 · answered Aug 30 '20 at 17:00

You could make use of a capturing group with an infinite quantifier inside a positive lookbehind. See Lookbehind in JS regular expressions for the browser support.

(?<=(\w+(?:\[\d+])+))(?=\[|$)

Explanation

(?<= Positive lookbehind, assert what is on the left is
- ( Capture group 1
  - \w+(?:\[\d+])+ Match 1+ word chars, and repeat 1+ times 1+ digits between square brackets
- ) Close group
) Close lookbehind
(?=\[|$) Positive lookahead, assert what is directly to the right is either [ or the end of the string

Regex demo

let regex = /(?<=(\w+(?:\[\d+])+))(?=\[|$)/g;

[
  "hello",
  "hello[0]",
  "hello[0][1]",
  "hello[0][1][3]",
  "hello[0][1][3][2]"
].forEach(s => {
  while ((m = regex.exec(s)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
      regex.lastIndex++;
    }
    console.log(m[1]);
  }
  console.log("-----------------");
});

Why is /.+\[[0-9]+\]/g not correctly splitting "hello[0][1][3]"

1 Answers1