JavaScript: String.prototype.matchAll

New in JS2020.

str.matchAll(regexObj_or_Str)

Returns a Iterable Object (is also an Iterator) of all occurrences and captures, or null if no match.

For each item in result, it is an array with meaning like this: [substring, capture1, capture2, etc]

• If argument is a regex object, it must have the flag g, else it's error. [see RegExp Flags]
• If argument is a string, it is converted to regex first by RegExp with added global flag g.

Example: Get Occurrences with Capture

const txt = "year 1999, 2010, and 2020";
const result = txt.matchAll(/\d{2}(\d{2})/g);

for (let k of result) {
  console.log(k);
};

// [ "1999", "99" ] ← 1st occurence, and its captures
// [ "2010", "10" ] ← 2nd occurence, and its captures
// [ "2020", "20" ] ← 3rd occurence, and its captures

const txt = "year 1999, 2010, and 2020";
const result = txt.matchAll(/\d{2}(\d{2})/g);

// to array
const arrayResult = [...result];

console.log(arrayResult[0]);
// [ "1999", "99" ]

console.log(arrayResult[1]);
// [ "2010", "10" ]

console.log(arrayResult[2]);
// [ "2020", "20" ]

Example: Get Occurrences, No Captures

// get all occurrences of year
const txt = "year 1999 and 2020";
const result = txt.matchAll(/\d{4}/g);

// to array
const arrayResult = [...result]

console.log(arrayResult);
// [ [ "1999" ], [ "2020" ] ]

If giving a RegExp Object as argument, it must have the global flag g

"year 1999".matchAll(/\d{4}/)
// error: Uncaught TypeError: String.prototype.matchAll called with a non-global RegExp argument

Showing Iterable and Iterator

const txt = "year 1999 and 2020";
const result = txt.matchAll(/\d{4}/g);

// result is a iterable
console.log(Reflect.has(result, Symbol.iterator));
// true

// result is a iterator
console.log(Reflect.has(result, "next"));
// true