blocks|key|4555579|text|这是因为尽管您将数组项的值更改为大写，但从未将该项设置回数组中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4555580|此代码不会更改原始数组项，而是创建一个大写的新字符串：|4555581|item.toUpperCase();|code-block|syntax|javascript|4555582|相反，循环遍历数组并将数组项设置为大写版本，如下所示：|4555583|​|4555584|let+arr+=+["new",+"name",+"need",+"test"]

for+(i+=+0;+i+<+arr.length;+i%2B%2B)+{
++arr[i]+=+arr[i].toUpperCase();
}

console.log(arr)|4555585|4555586|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|T|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|U|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|V|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|O|3|L|5|6|7|X|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|Q|$]]

<p>This is because although you change the value of the array item to upper case, you never set the item back in the array.</p>
<p>This code will <em>not</em> change the original array item, but will rather create a new string that is uppercase:</p>
<pre><code>item.toUpperCase();
</code></pre>
<p>Instead, loop through the array and set the array item to the upper case version like this:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arr = ["new", "name", "need", "test"]

for (i = 0; i &lt; arr.length; i++) {
  arr[i] = arr[i].toUpperCase();
}

console.log(arr)</code></pre>
</div>
</div>
</p>


blocks|key|3773323|text|toUpperCase返回一个新字符串，它不会改变字符串的位置。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3773324|​|3773325|let+arr+=+["new",+"name",+"need"]
const+newArr+=+[]
for+(let+item+of+arr)+{
++newArr.push(item.toUpperCase());
}

console.log(newArr)|code-block|syntax|javascript|3773326|3773327|您也可以在不使用map的显式循环的情况下进行同样的操作。|3773328|3773329|let+arr+=+["new",+"name",+"need"]
const+newArr+=+arr.map(item+=>+item.toUpperCase())
console.log(newArr);|3773330|3773331|entityMap^0|0|B|0|0|0|0|8|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Z|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|P|3|G|5|6|7|14|8|@]|D|@]|E|$]]|$1|Q|3|R|5|J|7|15|8|@]|D|@]|E|$K|L]]|$1|S|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|U|$]]

<p><code>toUpperCase</code> returns a new string, it does not change the string in place.</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arr = ["new", "name", "need"]
const newArr = []
for (let item of arr) {
  newArr.push(item.toUpperCase());
}

console.log(newArr)</code></pre>
</div>
</div>
</p>
<p>You can also do the same without an explicit loop using <code>map</code></p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arr = ["new", "name", "need"]
const newArr = arr.map(item =&gt; item.toUpperCase())
console.log(newArr);</code></pre>
</div>
</div>
</p>


blocks|key|1112885|text|你在任何地方都不能评价这种价值。你得把它分配到某个地方。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1112886|​|1112887|let+arr+=+["new",+"name",+"need"]
let+updatedArr+=+[];

for+(let+item+of+arr)+{
++const+value+=+item.toUpperCase();
++updatedArr.push(value);
}

console.log(updatedArr)+|code-block|syntax|javascript|1112888|1112889|或用map()简化解决方案|offset|length|style|CODE|1112890|1112891|const+arr+=+["new",+"name",+"need"]
const+updatedArr+=+arr.map(item=>item.toUpperCase());
console.log(updatedArr)++|1112892|1112893|entityMap^0|0|0|0|0|2|5|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|X|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|Z|8|@$L|10|M|11|N|O]]|9|@]|A|$]]|$1|P|3|C|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|13|8|@]|9|@]|A|$G|H]]|$1|S|3|C|5|6|7|14|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|U|$]]

<p>You are not assinging that value anywhere. You have to assign it somewhere.</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arr = ["new", "name", "need"]
let updatedArr = [];

for (let item of arr) {
  const value = item.toUpperCase();
  updatedArr.push(value);
}

console.log(updatedArr) </code></pre>
</div>
</div>
</p>
<p>or simplyfied solution with <code>map()</code>:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const arr = ["new", "name", "need"]
const updatedArr = arr.map(item=&gt;item.toUpperCase());
console.log(updatedArr)  </code></pre>
</div>
</div>
</p>


blocks|key|1116680|text|toUpperCase+返回字符串的上感知版本。它不会改变现有的字符串。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|1116681|您需要在某个地方分配返回值。|1116682|​|1116683|let+arr+=+["new",+"name",+"need"]

for+(let+i+=+0;+i+<+arr.length;+i%2B%2B)+{
++arr[i]+=+arr[i].toUpperCase();
}

console.log(arr);|code-block|syntax|javascript|1116684|1116685|entityMap^0|0|B|C|B|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|X|8|@]|E|@]|F|$]]|$1|I|3|J|5|6|7|Y|8|@]|E|@]|F|$]]|$1|K|3|L|5|M|7|Z|8|@]|E|@]|F|$N|O]]|$1|P|3|J|5|6|7|10|8|@]|E|@]|F|$]]|$1|Q|3|-4|5|6|7|11|8|@]|E|@]|F|$]]]|R|$]]

<p><code>toUpperCase</code> <strong>returns</strong> an uppercased version of a string. It doesn't mutate the existing string.</p>
<p>You need to assign the return value somewhere.</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arr = ["new", "name", "need"]

for (let i = 0; i &lt; arr.length; i++) {
  arr[i] = arr[i].toUpperCase();
}

console.log(arr);</code></pre>
</div>
</div>
</p>


blocks|key|3773448|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3773449|let+arr+=+["new",+"name",+"need"];
++++
arr+=+arr.map(item+=>+{
+++return+item.toUpperCase();
});
++++
console.log(arr);|code-block|syntax|javascript|3773450|3773451|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|K|8|@]|9|@]|A|$E|F]]|$1|G|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|M|8|@]|9|@]|A|$]]]|I|$]]

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="true">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arr = ["new", "name", "need"];
    
arr = arr.map(item =&gt; {
   return item.toUpperCase();
});
    
console.log(arr);</code></pre>
</div>
</div>
</p>


<pre><code>let arr = [&quot;new&quot;, &quot;name&quot;, &quot;need&quot;]

for (let item of arr) {
  item.toUpperCase();
}

console.log(arr)            /// [ 'new', 'name', 'need' ]

</code></pre>
<p>I am trying to create an array of UpperCased items using for of loop. However I keep getting the same array. What am I doing wrong?</p>


for of loop in javascript to create uppercased strings

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

let arr = ["new", "name", "need"]for (let item of arr) {  item.toUpperCase();}console.log(arr)            /// [ 'new', 'name', 'need' ]我正在尝试创建一个使用for循环的UpperCas...

问for of循环在javascript中创建上感知字符串
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问for of循环在javascript中创建上感知字符串EN