モジュールのレッスン (3/4)
コールバックに置き換える
If a replacement string is not enough, pass a function:
str.replace(regex, (match, ...groups) => string). The callback is invoked
for every match and its return value becomes the replacement.
'prezzi: 10 20 30'.replace(/\d+/g, (m) => Number(m) * 1.22);
// "prezzi: 12.2 24.4 36.6" (22% VAT)Callback arguments
str.replace(regex, (match, p1, p2, ..., offset, original, groups) => ...);match-- the entire match.p1,p2, \u2026 -- the captured groups in order.offset-- index of the match in the original string.original-- the whole string.groups-- object with the named groups (if any).
'2024-03-15'.replace(/(\d{4})-(\d{2})-(\d{2})/, (_, a, m, g) => `${g}/${m}/${a}`);
// "15/03/2024"The callback gives you arbitrary power: parsing, lookup, conversion, HTML escaping\u2026 everything that a static string cannot do.
Advanced arguments in replace callbacks
The callback function receives several arguments: the full match, each captured group, the offset of the match within the whole text, and the original input string. This enables sophisticated context-based transformation logic.
Try it
Find every integer in the text. (In replace you would pass `(m) => Number(m) * 2` to double it.)
ヒントを表示
Use \\d+ (one or more digits) to capture every integer as a single match.
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Review exercise
Find every email (simplified form: letters/digits/dots/underscores @ domain). This way a callback could redact it to `***@domain`.
ヒントを表示
Widen the class to [\\w.]+ to accept dots in the username and the domain.
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Additional challenge
Match every word consisting of letters in the text, so it can be transformed to uppercase via a callback.
ヒントを表示
Find simple letters with [a-zA-Z]+.
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