How to replace all single characters with some other one?

Question

JavaScript

For example, replace all 1s with 2. But if there are two 1s nearby, then do not replace them.
We try:

'aaa11aaaa1bbb1ccc1d1eeee'.replace(/([^1])1([^1])/g,'$12$2')

Result

"aaa11aaaa2bbb2ccc2d1eeee"

Oops, something went wrong. How to fix regex? The file is very large, not like in the example.

Answer 1

Something like that:

'aaa11aaaa1bbb1ccc1d1eeee'.replace(/(\D|^)([1]{1})((?=[a-zA-Z]|$))/g, '$12$3')

Answer 2

what went wrong is that c1d1eeeeafter replacing c1d with c2d , you still have 1eeee, which does not fall under the regular season, from the sequence.
try

'aaa11aaaa1bbb1ccc1d1eeee'.replace(/([^1])1{1}/g,'$12')

.