javascript - 理解を助けてください： onkey=Javascript</h1> <div id="body"><p>Please help me understand this line:</p> <p><code><textarea onkeyup='this.rows = (this.value.split("\n").length||1);' style="overflow-y: hidden;"><</a></h1> <div class="ml12 aside-cta flex--item print:d-none sm:ml0 sm:mb12 sm:order-first sm:as-end"> <a href="https://stackoverflow.com/questions/ask" target="_blank" class="ws-nowrap s-btn s-btnprimary">質問する</a></div> </div> <div class="d-flex fw-wrap pb8 mb16 bb bc-black-075"> <div class="flex--item ws-nowrap mr16 mb8"> <span class="fc-light mr2"></span> </div> <div class="flex--item ws-nowrap mr16 mb8" title="2022-04-17 15:46:40Z"> <span class="fc-light mr2">質問する</span> <time itemprop="dateCreated" datetime="2012-09-27T04:42:43.453">2012-09-27T04:42:43.453</time> </div> <div class="flex--item ws-nowrap mb8" title="Viewed 6 times"> <span class="fc-light mr2"></span> 151 次 </div> </div> <div id="mainbar" role="main" aria-label="question and answers"> <div class="question" 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js-gps-track" title="show questions tagged 'split'" rel="tag">split</a><a href="/tags/logical-operators" class="post-tag js-gps-track" title="show questions tagged 'logical-operators'" rel="tag">logical-operators</a> </div> </div> </div> </div> <span class="d-none" itemprop="commentCount">4</span> </div> </div> <div class="js-zone-container zone-container-responsive"> <div id="dfp-isb" class="everyonelovesstackoverflow everyonelovesinline-sidebar mx-auto" style="min-height: auto; height: auto; display: none;"></div> <div class="js-report-ad-button-container mx-auto" style="width: 300px"></div> </div> <div id="answers"> <a name="tab-top"></a> <div id="answers-header"> <div class="answers-subheader d-flex ai-center mb8"> <div class="flex--item fl1"> <h2 class="mb0" data-answercount=""> 1 に答える <span style="display:none;" itemprop="answerCount">1</span> </h2> </div> </div> </div> <a name="7"></a> <div id="answer-7" class="answer js-answer accepted-answer" data-answerid="7" data-parentid="4" data-score="506" data-position-on-page="1" data-highest-scored="1" data-question-has-accepted-highest-score="1" itemprop="suggestedAnswer" itemscope="" itemtype="https://schema.org/Answer"> <div class="post-layout"> <div class="votecell post-layout--left"> <div class="js-voting-container d-flex jc-center fd-column ai-stretch gs4 fc-black-200" data-post-id="7"> <button class="js-vote-up-btn flex--item s-btn s-btnunset c-pointer " data-controller="s-tooltip" data-s-tooltip-placement="right" aria-pressed="false" aria-label="Up vote" data-selected-classes="fc-theme-primary" data-unselected-classes="" aria-describedby="--stacks-s-tooltip-dgvag2l3"> <svg aria-hidden="true" class="svg-icon iconArrowUpLg" width="36" height="36" viewBox="0 0 36 36"><path d="M2 25h32L18 9 2 25Z"></path></svg> </button><div id="--stacks-s-tooltip-dgvag2l3" class="s-popover s-popovertooltip pe-none" aria-hidden="true" role="tooltip">This answer is useful<div class="s-popover--arrow"></div></div> <div class="js-vote-count flex--item d-flex fd-column ai-center fc-black-500 fs-title" itemprop="upvoteCount" data-value="1"> 1 </div> <button class="js-vote-down-btn flex--item s-btn s-btnunset c-pointer " data-controller="s-tooltip" data-s-tooltip-placement="right" aria-pressed="false" aria-label="Down vote" data-selected-classes="fc-theme-primary" data-unselected-classes="" aria-describedby="--stacks-s-tooltip-gn8ppsfv"> <svg aria-hidden="true" class="svg-icon iconArrowDownLg" width="36" height="36" viewBox="0 0 36 36"><path d="M2 11h32L18 27 2 11Z"></path></svg> </button> </div> </div> <div class="answercell post-layout--right"> <div class="s-prose js-post-body" itemprop="text"> <p><code>this.value</code>文字列値です。</p> <p>Javascript 文字列<code>split</code>には、文字列配列を返す関数があります。</p> <p>文字列配列には長さがあります。</p> <p>JavaScript では、0 は false として扱われます。</p> <p>したがって、<code>this.rows</code>入力を改行文字で分割した結果の文字列の数に等しく設定します。この数値が 0 の場合は、代わりに 1 に設定してください。</p> </div> <div class="mt24"> <div class="user-action-time" style="color:#999;text-align:right;">于 2012-09-27T04:47:49.620 に答える</div> </div> </div> </div> </div></div> </div> <div id="sidebar" class="show-votes" role="complementary" aria-label="sidebar"> <div class="module sidebar-related"> <h4 id="h-related">Related</h4> <div class="related js-gps-related-questions" data-tracker="rq=1"> <div class="spacer"> <a href="/questions/13810717" title="Question score (upvotes - downvotes)"> <div class="answer-votes large">3</div> </a> <a href="/questions/13810717" class="question-hyperlink">ldap - サブドメインを使用したグループメンバーシップの LDAP クエリ</a> </div><div class="spacer"> <a href="/questions/13810724" title="Question score (upvotes - downvotes)"> <div class="answer-votes large">1</div> </a> <a href="/questions/13810724" class="question-hyperlink">android - Android 入門ガイドの誤り</a> </div><div class="spacer"> <a href="/questions/13810731" title="Question score (upvotes - downvotes)"> <div class="answer-votes large">3</div> </a> <a 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