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Flags

RegExp flags and the properties that report them
Flag (property) Effect Flag (property) Effect
g (global) find all matches u (unicode) code points, \p{…} (ES2015)
i (ignoreCase) case-insensitive v (unicodeSets) u plus set operations (ES2024)
m (multiline) ^ $ match at line breaks y (sticky) match only at lastIndex
s (dotAll) . matches line breaks (ES2018) d (hasIndices) group positions (ES2022)

The v flag upgrades u (never combine them): classes gain subtraction --, intersection && and nesting, and \p{RGI_Emoji} matches whole multi-code-point emoji. Inline modifiers (ES2025, Baseline since September 2025) turn i, m or s on, or off with -, inside one group: (?i:…), (?-i:…). The engine builds d's indices only on request because they cost time.

The d and v flags and an inline modifierJavaScriptLive
const m = /(?<word>\w+)/d.exec('  hello');
console.log(m.indices[0], m.indices.groups.word);
console.log(/[\p{L}--\p{ASCII}]/v.test('é'), /[\p{L}--\p{ASCII}]/v.test('e'));
console.log(/^\p{RGI_Emoji}$/v.test('👍🏽'), /^\p{Emoji}$/u.test('👍🏽'));
const hello = /^Hello (?i:world)!$/;                  // i applies inside the group only
console.log(hello.test('Hello WORLD!'), hello.test('HELLO world!'));