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regexIgnoreCaseFlags

Reports regex patterns that can be simplified by using the i (ignore case) flag.

✅ This rule is included in the ts logical and logicalStrict presets.

When a character class contains both upper and lower case versions of the same letters, the pattern can be simplified by using the i (ignore case) flag. This makes the regex shorter and clearer by eliminating redundant character class entries.

Examples

Section titled “Examples”
AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0[a1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0[a-zA-1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0[aAbBc1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">
44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B<0[a] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fi spans="tyle--0:#D6DEEB;--1:#40">3<]/i><;di vdivclass="Nameexpressive-">44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fi spans="tyle--0:#D6DEEB;--1:#40">3<]/i><;di vdivclass="Nameexpressive-">44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fi spans="tyle--0:#D6DEEB;--1:#40">3<]/i><;di vdivclass="Nameexpressive-">6376// Only lowercase letters - no redund44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#D6DEEB;--1:#40">3<;di vdivclass="Nameexpressive-">6376// Only uppercase letters - no redund44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#D6DEEB;--1:#40">3<;di vdivclass="Nameexpressive-">6376// Already using the i 44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fi spans="tyle--0:#D6DEEB;--1:#40">3<]/i>

Options

Section titled “Options”

This rule is not configurable.

When Not To Use It

Section titled “When Not To Use It”

If you need explicit control over case matching in your regex patterns, or if your codebase intentionally avoids the i flag for performance or compatibility reasons, you might prefer to disable this rule. Some legacy JavaScript environments may have inconsistent behavior with the i flag for non-ASCII characters.

Further Reading

Section titled “Further Reading”

Equivalents in Other Linters

Section titled “Equivalents in Other Linters”