What is lookbehind support in JS? How to replace it?

Question

I have a string and I want to replace every 'i' that is NOT following/followed by any other i and replace it with 'z`. I know that there is negative lookahead and lookbehind.

Results shoud be:

i => z
iki => zkz
iiki => iikz
ii => ii
iii => iii

I tried to use this:

/(?<!i)i(?!i)/gi

and it failed and thrown an error: Invalid regex group.

Yet

/i(?!i)/gi

works fine, but matches second "i" in this: "ii".

Is there some other way?

What is support for lookbehind in JS if there is any?

Answer 1

In your case you don't really need look-behind:

'iiki'.replace(/i+/g, (m0) => m0.length > 1 ? m0 : 'z')

You can just use a function as the replacement part and test the length of the matched string.

Here are all your test cases:

function test(input, expect) {
  const result = input.replace(/i+/g, (m0) => m0.length > 1 ? m0 : 'z');
  console.log(input + " => " + result + " // " + (result === expect ? "Good" : "ERROR"));
}

test('i', 'z');
test('iki', 'zkz');
test('iiki', 'iikz');
test('ii', 'ii');
test('iii', 'iii');