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getElementsByClassNameの結果に対してforEachやmapを使う方法

Last updated at Posted at 2018-09-15

まずgetElementsByClassNameでHTMLCollectionを取得します

var elements = document.getElementsByClassName( "sample" );

HTMLCollectionに対してforEachを使うと

elements.forEach(x => console.log(x)); // Uncaught TypeError

Uncaught TypeError: elements.forEach is not a function というエラーが発生します。

HTMLCollectionは配列ではないので、forEachやmapは利用できないらしいです。

forEachやmapを使いたかったので配列に変換します。

elements = Array.from( elements ) ;

これで配列に変換できたのでforEachやmapなどが使えるようになりました。

elements.forEach(x => console.log(x));
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