Split a string with regular expression lookarounds using javascript

Question

I want to use String.prototype.split to split the string if the previous character is not equal to the next character, here's the target result:

'abcd' => ['a', 'b', 'c', 'd']

'aaabbbccd' => ['aaa', 'bbb', 'cc', 'd']

I know it's possible to split a string by only lookbacks :

 const result = 'aaabbbccd'.split(/(?<=a)/); console.log(result); // ["a", "a", "a", "bbbccd"]

So I wanted to find an expression to find the delimiter of two characters that its lookback is not equal to lookahead.

But I tried this, and it doesn't work:

 const result = 'aaabbcccd'.split(/(?<!\\2)(?=.)/); console.log(result); // ['a', 'a', 'a', 'b', 'b', 'c', 'c', 'c', 'd']

So is there a regular expression to achieve this? Or it's just simply impossible to do that with regex?

Answer 1

Using backreferences, you can use .match() instead of .split() to get your desired result like so:

 const r1 = 'abcd'.match(/(.)\\1*/g); const r2 = 'aaabbcccd'.match(/(.)\\1*/g); console.log(r1); // ['a', 'b', 'c', 'd'] console.log(r2); // ['aaa', 'bb', 'ccc', 'd']

This will match any character (.) , followed by the same character \\1 zero or more times