Examples
Subexpressions
When the regular expression contains subexpressions grouped with parentheses, the text that matched those groups will also show up in the array. The whole match is always the first element. The next element is the part matched by the first group (the one whose opening parenthesis comes first in the expression), then the second group, and so on.
let quotedText = /'([^']*)'/;
console.log(quotedText.exec("she said 'hello'"));No matches
When a group does not end up being matched at all (for example, when followed by a question mark), its position in the output array will hold undefined. Similarly, when a group is matched multiple times, only the last match ends up in the array.
console.log(/bad(ly)?/.exec("bad"));
console.log(/(\d)+/.exec("123"));