【JavaScript】 replace()の使い方 単純な置換と正規表現での置換

例：最初の一つだけ置換

const text = "abcdefg abcdefg";
const result = text.replace( "def" , "---");
console.log( result); // abc---g abcdefg

例：全て置換

const text = "abcdefg abcdefg";
const result = text.replace( /def/g , "---"); // 正規表現部分に""はつけない
console.log( result); // abc---g abc---g

例：大文字と小文字を区別しないで全て置換

const text = "abcdefg abcDeFg";
const result = text.replace( /def/gi , "---");
console.log( result); // abc---g abc---g

const data = "今日東京は快晴です！しかし残念ながら明日は快晴となるでしょう。";
const result = data.replace( /(.*)快晴/ , "$1豪雨" );
console.log( result ); // 今日東京は快晴です！しかし残念ながら明日は豪雨となるでしょう。

例：複数の文字列を置換

const text = "abcdefg abcdefg";
const result = text.replace( /def/g , "DEF").replace( /ab/g , "AB");
console.log( result );    // ABcDEFg ABcDEFg

例

const text = "abcdefg abcdefg";
const result = text.replace( /def/g , "[$&]");
console.log( result); // abc[def]g abc[def]g

const text = "abc1defg abc2defg";
const result = text.replace( /(c\d)(def)/g , ( p0 , p1 , p2 )=>{
            return " ★ [" + p0 + "] → [" + p1 + p2.toUpperCase() + "] ★ ";
});
console.log( result); // ab ★ [c1def] → [c1DEF] ★ g ab ★ [c2def] → [c2DEF] ★ g

レスト構文で引数を配列に集約

const result = text.replace( /(c\d)(def)/g , ( ...arg )=>{
            const length = arg.length;
            const index = arg[length - 2];
            const input = arg[length - 1];
            return "index:" + index + " input:" + input;
        });

text.replace( /\r|\r\n/g ,  "\n" )
または
text.replace( /\r\n?/g ,  "\n" )

text.replace( /\r|\n|\r\n/g ,  "<br>" )

text.replace( /\r|\n|\r\n/g ,  "<>" )

text.replace( / /g ,  "　" )

text.replace( /　/g ,  " " )

const baseValue = "！".charCodeAt(0) - "!".charCodeAt(0);

const result = data.replace( /[!-~]/g ,
            (v) => String.fromCharCode(v.charCodeAt(0) + baseValue)
        );

const baseValue = "！".charCodeAt(0) - "!".charCodeAt(0);

const result = data2.replace(/[！-～]/g,
            (v) => String.fromCharCode(v.charCodeAt(0) - baseValue)
        );

const kanaZenkaku = [
            "ア","イ","ウ","エ","オ","カ","キ","ク","ケ","コ","サ","シ","ス","セ","ソ",
            "タ","チ","ツ","テ","ト","ナ","ニ","ヌ","ネ","ノ","ハ","ヒ","フ","ヘ","ホ",
            "マ","ミ","ム","メ","モ","ヤ","ユ","ヨ","ラ","リ","ル","レ","ロ",
            "ワ","ヰ","ヱ","ヲ","ン",
            "ガ","ギ","グ","ゲ","ゴ","ザ","ジ","ズ","ゼ","ゾ","ダ","ヂ","ヅ","デ","ド",
            "バ","ビ","ブ","ベ","ボ","パ","ピ","プ","ペ","ポ",
            "ァ","ィ","ゥ","ェ","ォ","ャ","ュ","ョ","ッ"
];
kanaZenkaku.reg = new RegExp( "(" + kanaZenkaku.join("|") + ")" , "g");

const kanaHankaku = [
            "ｱ","ｲ","ｳ","ｴ","ｵ","ｶ","ｷ","ｸ","ｹ","ｺ","ｻ","ｼ","ｽ","ｾ","ｿ",
            "ﾀ","ﾁ","ﾂ","ﾃ","ﾄ", "ﾅ","ﾆ","ﾇ","ﾈ","ﾉ","ﾊ","ﾋ","ﾌ","ﾍ","ﾎ",
            "ﾏ","ﾐ","ﾑ","ﾒ","ﾓ","ﾔ","ﾕ","ﾖ","ﾗ","ﾘ","ﾙ","ﾚ","ﾛ",
            "ﾜ","ｲ","ｴ","ｦ","ﾝ",
            "ｶﾞ","ｷﾞ","ｸﾞ","ｹﾞ","ｺﾞ","ｻﾞ","ｼﾞ","ｽﾞ","ｾﾞ","ｿﾞ","ﾀﾞ","ﾁﾞ","ﾂﾞ","ﾃﾞ","ﾄﾞ",
            "ﾊﾞ","ﾋﾞ","ﾌﾞ","ﾍﾞ","ﾎﾞ","ﾊﾟ","ﾋﾟ","ﾌﾟ","ﾍﾟ","ﾎﾟ",
            "ｧ","ｨ","ｩ","ｪ","ｫ","ｬ","ｭ","ｮ","ｯ"
        ];
kanaHankaku.reg = new RegExp( "(" + kanaHankaku.join("|") + ")" , "g");

const hiragana = [
            "あ","い","う","え","お","か","き","く","け","こ","さ","し","す","せ","そ",
            "た","ち","つ","て","と", "な","に","ぬ","ね","の","は","ひ","ふ","へ","ほ","ま",
            "み","む","め","も","や","ゆ","よ", "ら","り","る","れ","ろ",
            "わ","ヰ","ゑ","を","ん",
            "が","ぎ","ぐ","げ","ご","ざ","じ","ず","ぜ","ぞ","だ","ぢ","づ","で","ど",
            "ば","び","ぶ","べ","ぼ","ぱ","ぴ","ぷ","ぺ","ぽ",
            "ぁ","ぃ","ぅ","ぇ","ぉ","ゃ","ゅ","ょ","っ"
        ];
hiragana.reg = new RegExp( "(" + hiragana.join("|") + ")" , "g");

function kanaConv( text , formArray , toArray ) {
            return text.replace(formArray.reg,
                (v) => {
                    return toArray[ formArray.indexOf( v ) ];
                }
            );
}

const text = "ｱｲｳｴｵｶｷｸｹｺ";
const result = kanaConv( text , kanaHankaku , kanaZenkaku  );
console.log( result ); // アイウエオカクキケコ

const text = "アイウエオカクキケコ";
const result = kanaConv( text , kanaZenkaku , kanaHankaku  );
console.log( result ); // ｱｲｳｴｵｶｷｸｹｺ

const text = "ｱｲｳｴｵｶｷｸｹｺ";
const result = kanaConv( text , kanaHankaku , hiragana   );
console.log( result ); // あいうえおかきくけこ

const text = "アイウエオカクキケコ";
const result = kanaConv( text , kanaHankaku , hiragana   );
console.log( result ); // あいうえおかきくけこ

const text ="1個3000.25円のリンゴを20000個購入した。総額60005000円だ。";
const result = text.replace(/\d\d\d\d+/g, // (1)
            ( val ) =>{                
                    return  val.replace(/(\d)(?=(\d\d\d)+$)/g, "$1,"); // (2)
            }
        );
console.log( result ); // 1個3,000.25円のリンゴを20,000個購入した。総額60,005,000円だ。