To match consecutively repeating characters in a string, you can simply use a regular expression that uses a backreference to the same character that's matched in a capturing group.
For example, to match letters that appear consecutively in a string, you can do the following:
const str = 'aabbcccdde'; const pattern = /([a-z])\1+/g; const matches = str.match(pattern); console.log(matches); // ['aa', 'bb', 'ccc', 'dd']
In the example above, the capturing group matches characters a-z only once. Then right after, using a backreference to the capturing group (i.e. \1 — which refers to the first capturing group), the same character is matched again, one or more times. As a result, it matches characters that appear in the string consecutively.
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