var a=[1,2,3,4,5] //jQuery $.each(a,function(){ console.log(this); //1,2,3,4,5が、Numberクラスに変換されて表示される }); //forEach a.forEach(function(val){ console.log(this); //undefinedが表示されるか、windowオブジェクトが表示される }); var b = [5,6,7,8,9] a.forEach(function(val,index){ console.log(this[index]); //5,6,7,8,9が表示される },b);
![JavaScript Array.forEachとjQuery.eachの違い - Qiita](https://cdn-ak-scissors.b.st-hatena.com/image/square/d306a54709973418f8318661ae538545e3aed710/height=288;version=1;width=512/https%3A%2F%2Fqiita-user-contents.imgix.net%2Fhttps%253A%252F%252Fcdn.qiita.com%252Fassets%252Fpublic%252Farticle-ogp-background-412672c5f0600ab9a64263b751f1bc81.png%3Fixlib%3Drb-4.0.0%26w%3D1200%26mark64%3DaHR0cHM6Ly9xaWl0YS11c2VyLWNvbnRlbnRzLmltZ2l4Lm5ldC9-dGV4dD9peGxpYj1yYi00LjAuMCZ3PTk3MiZoPTM3OCZ0eHQ9SmF2YVNjcmlwdCUyMEFycmF5LmZvckVhY2glRTMlODElQThqUXVlcnkuZWFjaCVFMyU4MSVBRSVFOSU4MSU5NSVFMyU4MSU4NCZ0eHQtYWxpZ249bGVmdCUyQ3RvcCZ0eHQtY29sb3I9JTIzMjEyMTIxJnR4dC1mb250PUhpcmFnaW5vJTIwU2FucyUyMFc2JnR4dC1zaXplPTU2JnM9MWVhZTk4ZjFhOTBkZTZmNjkzYWY2YmIxNzExY2EyOGU%26mark-x%3D142%26mark-y%3D57%26blend64%3DaHR0cHM6Ly9xaWl0YS11c2VyLWNvbnRlbnRzLmltZ2l4Lm5ldC9-dGV4dD9peGxpYj1yYi00LjAuMCZoPTc2Jnc9NzcwJnR4dD0lNDBQaWFub1Njb3JlSlAmdHh0LWNvbG9yPSUyMzIxMjEyMSZ0eHQtZm9udD1IaXJhZ2lubyUyMFNhbnMlMjBXNiZ0eHQtc2l6ZT0zNiZ0eHQtYWxpZ249bGVmdCUyQ3RvcCZzPWRiN2Y0ZTljYzkzOWMyZTkyN2Q0NDEwYzhjOTJjOGYy%26blend-x%3D142%26blend-y%3D486%26blend-mode%3Dnormal%26s%3Dc4da16f109a88ac0208b4ad4db05fa32)