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class="task__title-wrap"><h2 class="task__title">Finally or just the code?</h2></div><div class="task__header-note"><span class="task__importance" title="タスクの重要度を表し、1 から 5 までです">重要性: 5</span></div></div><div class="task__content"><div class="task__formatted"><p>2つのコードの断片を比較してみてください。</p> <ol> <li> <p>1つ目は <code>try..catch</code> のあとにコードを実行するために <code>finally</code> を使います:</p> <div id="pkm9yglxh7" data-trusted="1" class="code-example" data-highlight="[{"start":5,"end":5}]"> <div class="codebox code-example__codebox"> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>try { work work } catch (e) { handle errors } finally { 作業場所のクリーンアップ }</code></pre> </div> </div> </div></li> <li> <p>2つ目は <code>try..catch</code> の直後にクリーンアップする処理を置きます:</p> <div id="1hh3k7ju4d" data-trusted="1" class="code-example" data-highlight="[{"start":6,"end":6}]"> <div class="codebox code-example__codebox"> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>try { work work } catch (e) { handle errors } 作業場所のクリーンアップ</code></pre> </div> </div> </div></li> </ol> <p>私たちは、処理が開始された後には、それがエラーかどうかは関係なく必ずクリーンアップが必要です。</p> <p><code>finally</code> を使うことの利点はあるでしょうか？それとも両方のコードは同じでしょうか？もし利点がある場合はそれが関係する例を挙げてください。</p> </div><button class="task__solution" type="button">解答</button><div class="task__answer"><div class="task__answer-content"><div class="formatted"><p>その違いは、関数内のコードを見ると明らかになります。</p> <p>もし <code>try..catch</code> の “飛び出し” がある場合、振る舞いは異なります。</p> <p>例えば、<code>try..catch</code> の中で <code>return</code> がある場合です。<code>finally</code> 句は <code>try..catch</code> が <em>どのような終わり方の場合にでも</em> 動作します。たとえ、<code>return</code> 文経由でさえも。</p> <div id="dkkax7sf9f" data-trusted="1" class="code-example" data-highlight="[{"start":3,"end":3}]"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="実行" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="サンドボックで開く" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>function f() { try { alert('start'); return "result"; } catch (e) { /// ... } finally { alert('cleanup!'); } } f(); // cleanup!</code></pre> </div> </div> </div><p>…もしくは次のように <code>throw</code> がある場合:</p> <div id="ciyutzhd5w" data-trusted="1" class="code-example" data-highlight="[{"start":7,"end":7}]"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="実行" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="サンドボックで開く" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>function f() { try { alert('start'); throw new Error("an error"); } catch (e) { // ... if("can't handle the error") { throw e; } } finally { alert('cleanup!') } } f(); // cleanup!</code></pre> </div> </div> </div><p>ここで <code>finally</code> はクリーンアップを保証します。もし <code>f</code> の終わりにコードをおいた場合は実行されない場合があります。</p> </div></div><button class="close-button task__answer-close" type="button" title="閉じる"></button></div></div></div></div></main></div></div></div><div class="page-footer"><ul class="page-footer__list"><li class="page-footer__item page-footer__item_copy">© 2007—2025 Ilya Kantor</li><li class="page-footer__item page-footer__item_about"><a class="page-footer__link" href="/about">プロジェクトについて</a></li><li class="page-footer__item page-footer__item_contact"><a class="page-footer__link" href="/about#contact-us">コンタクト</a></li></ul></div></body></html>