JavaScript - Compare the Case Insensitive Strings Last Updated : 26 Nov, 2024 Comments Improve Suggest changes Like Article Like Report Here are the different methods to compare the case-insensitive strings in JavaScript.1. Using toLowerCase() or toUpperCase() MethodsThis is the most simple and used approach. Convert both strings to the same case and then compare them. JavaScript const comStr = (s1, s2) => s1.toLowerCase() === s2.toLowerCase(); const s1 = "Hello"; const s2 = "hello"; console.log(comStr(s1, s2)); Outputtrue Both strings are converted to lowercase (or uppercase), ensuring the comparison ignores case differences.2. Using localeCompare() MethodThe localeCompare() method provides a built-in way to compare strings while ignoring case differences. JavaScript const comStr = (s1, s22) => s1.localeCompare(s2, undefined, { sensitivity: 'accent' }) === 0; const s1 = "Hello"; const s2 = "hello"; console.log(comStr(s1, s2)); Outputtrue The sensitivity: 'accent' option ensures the comparison is case-insensitive but respects accents if present.3. Using Regular ExpressionsYou can use a regular expression with the i flag (case-insensitive) to match strings. JavaScript const comStr = (s1, s2) => new RegExp(`^${s1}$`, "i").test(s2); const s1 = "Hello"; const s2 = "hello"; console.log(comStr(s1, s2)); Outputtrue This method is useful for pattern-based comparisons but may not be as efficient for simple equality checks.4. Using normalize() for Unicode StringsWhen dealing with strings containing special characters or accents, normalize() can be combined with toLowerCase() for accurate comparison. JavaScript const comStr = (s1, s2) => s1.normalize("NFD").toLowerCase() === s2.normalize("NFD").toLowerCase(); const s1 = "héllo"; const s2 = "HÉLLO"; console.log(comStr(s1, s2)); Outputtrue This approach ensures case-insensitive comparison while handling Unicode normalization.5. Using Array.every() with Character-by-Character ComparisonSplit the strings into arrays of characters and compare each character case-insensitively. JavaScript const comStr = (s1, s2) => s1.length === s2.length && [...s1].every((char, index) => char.toLowerCase() === s2[index].toLowerCase()); const s1 = "Hello"; const s2 = "hello"; console.log(comStr(s1, s2)); Outputtrue This is less efficient but can be useful when you need additional processing for each character.Which Approach Should You Use?ApproachWhen to UseUsing toLowerCase()Best for simplicity and efficiency in most scenarios.Using localeCompare()Ideal for multilingual applications or locale-sensitive comparisons.Using Regular ExpressionsUse for pattern-based comparisons or dynamic matching.Using normalize()Essential for strings with accents or Unicode characters.Character-by-CharacterUse for custom logic or additional character-level processing.Among these, toLowerCase() and localeCompare() are the most widely used and efficient for case-insensitive string comparison in JavaScript. 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