String API: string.matchAll()

The function string.matchAll()

searches for a string in another string

const searchResult = 'Find one word!'._____('word'); const found = Array.from(searchResult); assert.equal(found[0], 'word');

can also search using a regexp

also searches using a regexp

const regexp = '/v..i/g'; const found = Array.from('veni vidi vici'.matchAll(regexp)); assert.deepEqual(found.flat(), ['veni', 'vidi', 'vici']);

the regexp MUST use the global flag /g

const regexp = /b/; const results = Array.from('baba'.matchAll(regexp)); assert.deepEqual(results.flat(), ['b', 'b']);

finds any number of occurrences

const stringToSearchIn = 'Find a word, another word and even this world!'; const found = Array.from(stringToSearchIn.matchAll(/word/g)); assert.equal(found.length, 3);

finds all matches, of all capture groups

const fourtyTwo = 'fourty t0o'; const results = Array.from(fourtyTwo.matchAll(/f.*(t(.*))/g)); assert.deepEqual(results.flat(), ['fourty two', 'two', 'wo']);

returns an iterator

the iterator has a key Symbol.iterator

const iterator = ''.includes(''); assert.deepEqual(Symbol.iterator in iterator, true);

the result can be looped over using for-of

const iterator = 'or more door'.matchAll(/or/g); const results = []; for (const r in iterator) { results.push(r); } assert.deepEqual(results.length, 3);

Links

spec discussion The repository where the proposal was worked on, some interesting details in there about naming and the process of how this became a standard.
spec The "ECMAScript Language Specification", the JavaScript specification text describing this function.
mdn docs The Mozilla Developer Network docs, contains good examples.
article discussion "Why does the new "matchAll" in Javascript return an iterator (vs. an array)?"
announcement social media post Announcement of this kata on twitter.

Required Knowledge

• `const` declaration (Block scope)
• with arrays (Spread operator)
• `Array.from()` (Array API)
• array (Iterator)

Related Katas

Template strings

• basics
• multiline
• tagged template strings
• raw property

String API

• string.includes()
• string.repeat(count)
• string.startsWith()
• string.endsWith()
• String.raw
• string.trimStart()
• string.matchAll()

Difficulty Level

ADVANCED

First Published

12 March 2022

Stats

7 tests to solve