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38 lines
1.8 KiB
TypeScript
38 lines
1.8 KiB
TypeScript
// $<name> in replace/replaceAll templates (GetSubstitution's named arm)
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// and \k<name> backreferences in patterns.
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console.log("2024-07-15".replace(/(?<y>\d{4})-(?<m>\d{2})-(?<d>\d{2})/, "$<m>/$<d>/$<y>"));
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console.log("a1b2c3".replace(/(?<digit>\d)/g, "[$<digit>]"));
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console.log("a1b2c3".replaceAll(/(?<digit>\d)/g, "<$<digit>>"));
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// Mixed numbered and named references in one template.
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console.log("john smith".replace(/(?<first>\w+) (\w+)/, "$2, $<first> ($1 $2)"));
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// A nonexistent group name substitutes empty (Get → undefined → "").
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console.log("a".replace(/(?<x>a)/, "[$<x>][$<nope>]"));
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// No named groups in the pattern → namedCaptures is undefined and $< is
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// literal; an unterminated $<name is literal even WITH named groups.
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console.log("a".replace(/a/, "[$<x>]"));
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console.log("a".replace(/(?<x>a)/, "[$<x]"));
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// A nonparticipating named group substitutes empty; duplicates across
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// alternatives resolve to the participating occurrence.
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console.log("ab".replace(/(?<a>a)|(?<b>b)/g, "<$<a>|$<b>>"));
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console.log("14px 9em".replace(/(?<n>\d+)px|(?<n>\d+)em/g, "[$<n>]"));
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// $` and $' still compose around named references.
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console.log("xyz".replace(/(?<mid>y)/, "($`|$<mid>|$')"));
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// \k<name> backreferences: quote matching, case-insensitive reuse.
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const quoted = /(?<q>['"]).*?\k<q>/;
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console.log(quoted.test('say "hi" ok'), quoted.test("say 'hi ok"));
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console.log(/(?<tag>[a-z]+)-\k<tag>/i.test("Abc-ABC"), /(?<tag>[a-z]+)-\k<tag>/.test("abc-xyz"));
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console.log("noon moon".replace(/(?<c>[a-z])\k<c>/g, "[$<c>$<c>]"));
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// Named groups under /u with non-ASCII subjects: UTF-16-exact slices.
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console.log("héllo wörld".replace(/(?<w>\wö\w+)/u, "«$<w>»"));
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// source/flags of a named-group regex are the literal's own text.
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const re = /(?<a>x)\k<a>/gi;
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console.log(re.source, re.flags);
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