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String.prototype.toLowerCase() - JavaScript | MDN
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String.prototype.toLowerCase()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2015年7月.
toLowerCase() は String 値のメソッドで、呼び出す文字列の値を小文字に変換して返します。
試してみましょう
const sentence = "The quick brown fox jumps over the lazy dog.";
console.log(sentence.toLowerCase());
// 予想される結果: "the quick brown fox jumps over the lazy dog."
構文
js
toLowerCase()
引数
なし。
返値
呼び出す文字列の値を小文字に変換した新しい文字列です。
解説
toLowerCase() メソッドは、小文字に変換された文字列の値を返します。toLowerCase() メソッドは、文字列 str 自身の値には影響を与えません。
例
toLowerCase() メソッドの使用
js
console.log("ALPHABET".toLowerCase()); // 'alphabet'
仕様書
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-string.prototype.tolowercase |
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