match-vs-exec-g.md

match() vs. exec() and RegExp with/without the g Flag

Summary

	RegExp without g	RegExp with g
match()	[WHOLE_MATCH_1, ...MATCH_1_GROUPS]	[WHOLE_MATCH_1, WHOLE_MATCH_2 ...]
exec()	[WHOLE_MATCH_1, ...MATCH_1_GROUPS]	[WHOLE_MATCH_N, ...MATCH_N_GROUPS], null if there's no more matches (another call repeats the process)

RegExp without the g Flag

match()

const str = 'A1aB2bC3cD4d';
const re = /([A-Z])[0-9]([a-z])/;

str.match(re);
// ['A1a', 'A', 'a']

str.match(re);
// ['A1a', 'A', 'a']

exec()

const str = 'A1aB2bC3cD4d';
const re = /([A-Z])[0-9]([a-z])/;

re.exec(str);
// ['A1a', 'A', 'a']

re.exec(str);
// ['A1a', 'A', 'a']

RegExp with the g Flag

match()

const str = 'A1aB2bC3cD4d';
const re = /([A-Z])[0-9]([a-z])/g;

str.match(re);
// ['A1a', 'B2b', 'C3c', 'D4d']

str.match(re);
// ['A1a', 'B2b', 'C3c', 'D4d']

exec()

const str = 'A1aB2bC3cD4d';
const re = /([A-Z])[0-9]([a-z])/g;

re.exec(str);
// ['A1a', 'A', 'a']
re.exec(str);
// ['B2b', 'B', 'b']
re.exec(str);
// ['C3c', 'C', 'c']
re.exec(str);
// ['D4d', 'D', 'd']
re.exec(str);
// null

re.exec(str);
// ['A1a', 'A', 'a']
// ...

• use with while loop:

let match;
while(match = re.exec(str)) {
  console.log(match);
}

// ['A1a', 'A', 'a']
// ['B2b', 'B', 'b']
// ['C3c', 'C', 'c']
// ['D4d', 'D', 'd']

• use with for loop:

for (let match; match !== null; match = re.exec(str)) {
  console.log(match);
}

// ['A1a', 'A', 'a']
// ['B2b', 'B', 'b']
// ['C3c', 'C', 'c']
// ['D4d', 'D', 'd']

for (let match; (match = re.exec(str)) !== null; ) {
  console.log(match);
}

// ['A1a', 'A', 'a']
// ['B2b', 'B', 'b']
// ['C3c', 'C', 'c']
// ['D4d', 'D', 'd']