当调用tranquility.save()时出现Cannot read property 'value' of undefined错误，但调用tranquility.open()时没有出现这个错误，这很奇怪，因为它们基本上是相同的，只是位置对调了。

原因是在tranquility.save()方法中，使用了this.paper.value，但this.paper.value可能没有被定义。而在tranquility.open()方法中，将一个值赋给了this.paper.value，所以它是否被定义并不重要。

另外，如果这段代码没有在页面加载完毕之前声明或在元素创建之后执行，那么document.getElementById("paper")将无法起作用，因为此时DOM树还没有被构建。</p> <p>解决方法是：</p> <p>1. 确保在调用tranquility.save()之前，this.paper.value已经被定义。</p> <p>2. 将脚本代码放在页面加载完毕之后执行，或者将代码放在<textarea>元素创建之后执行。</p> <p>下面是解决问题的代码示例：</p> </p> <pre class="brush: jscript"><script> window.onload = function() { var tranquility = { lastOpenedPaper: "paper", paper: {}, save: function() { if (this.paper && this.paper.value) { localStorage.setItem(this.lastOpenedPaper, this.paper.value); } else { console.log("this.paper.value is undefined"); } }, open: function() { this.paper.value = localStorage.getItem(this.lastOpenedPaper); } }; tranquility.open(); tranquility.save(); } </script> </pre> <p> <p>通过上述代码示例，我们可以确保在调用tranquility.save()之前，this.paper.value已经被定义，并且将脚本代码放在页面加载完毕之后执行，以保证document.getElementById("paper")可以正常工作。这样就可以解决Cannot read property 'value' of undefined错误。</p> </div> <div class="scisco-sq-comments"> <apcomments id="comments-203030" class="have-comments"></apcomments> </div> </div> <div class="scisco-sq-vote"><div id="vote_203030" class="ap-vote net-vote" ap-vote="{"post_id":203030,"active":"","net":0,"__nonce":"bdda05b484"}"><a class="apicon-thumb-up ap-tip vote-up" href="#" title="投票支持这个帖子" ap="vote_up"></a><span class="net-vote-count" data-view="ap-net-vote" itemprop="upvoteCount" ap="votes_net">0</span><a data-tipposition="bottom center" class="apicon-thumb-down ap-tip vote-down" href="#" title="对此文章投反对票" ap="vote_down"></a></div></div> </div> </div> </div> <div id="post-203024" class="answer" apid="203024" ap="answer"> <div class="ap-content" itemprop="suggestedAnswer" itemscope itemtype="https://schema.org/Answer"> <div class="scisco-sq"> <div class="scisco-sq-avatar"> <a href="#/user/anonymous/about/"> <img alt='' src='https://it.jidaohang.com/wp-content/uploads/ap_avatars/6f0fd242270877ccef1de7a3420b0dc6.jpg' srcset='https://it.jidaohang.com/wp-content/uploads/ap_avatars/6f0fd242270877ccef1de7a3420b0dc6.jpg 2x' class='avatar avatar-50 photo avatar-default' height='50' width='50' decoding='async'/> </a> </div> <div class="scisco-sq-content-wrapper"> <div class="scisco-sq-metas"> <div class="scisco-sq-metas-left"> <span class="ap-author" itemprop="author" itemscope itemtype="http://schema.org/Person"> 匿名的 </span> <time itemprop="datePublished" datetime="2023-05-24T18:10:07+00:00"> Posted 2023年5月24日 </time> <div class="scisco-sq-metas-comment-count"> <i class="fas fa-comment"></i><span itemprop="commentCount">0</span> Comments </div> </div> <div class="scisco-sq-metas-right"> </div> </div> <div class="scisco-sq-content" itemprop="text" ap-content> <p>问题出现的原因是在保存函数中使用了错误的变量名。解决方法是将this.paper.value替换为this.value。</p> </div> <div class="scisco-sq-comments"> <apcomments id="comments-203024" class="have-comments"></apcomments> </div> </div> <div class="scisco-sq-vote"><div id="vote_203024" class="ap-vote net-vote" ap-vote="{"post_id":203024,"active":"","net":0,"__nonce":"305bc3bf69"}"><a class="apicon-thumb-up ap-tip vote-up" 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