blocks|key|597959|text|正如MDN规范中详细介绍的那样，let正在从数组元素的副本中声明一个新变量。因此，更改v不会更改数组中的值。这是var和const共享的，只是javascripts的行为而已。当您创建一个新对象时，它将开始为空。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|597960|您的循环基本上是说：“对于arr中的每个元素，声明一个保存其副本的变量，然后如果该变量是c，则将该副本更改为f”。|597961|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let^0|G|3|17|1|1K|3|1O|5|2|3|0|0|D|3|18|1|1I|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@$9|Y|A|Z|1|10]]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

As detailed in the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let" rel="nofollow">MDN</a> spec, <code>let</code> is declaring a new variable from a copy of your array element. So changing the <code>v</code> will not change the value in the array. This is shared by <code>var</code> and <code>const</code> and is simply just javascripts behaviour. When you create a new object, it starts empty.

Your loop is basically saying "For every element in <code>arr</code>, declare a variable holding a copy of it and then if that variable is <code>c</code>, change that copy to <code>f</code>"

blocks|key|324764|text|Javascript不创建对简单值(如String+)的引用。要获得数组引用，您需要让数组是像[{char+:+'a'},+{char+:+'b'},+...]这样的对象数组。然后，在迭代器中，您可以通过更改char属性来更改数组元素。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|324765|let+arr+=+[{char:+'a'},+{char+:'b'},+...];

for+(let+v+of+arr)+{
++++if+(v.char+===+'c')++{
++++++v.char+=+'f';
++++++break;
++++}+++++++
}|code-block|syntax|javascript|324766|entityMap^0|J|6|1B|X|2W|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

Javascript does not create references to simple values such <code>String</code>. To get array referrenced, you need to let array be an array of objects like <code>[{char : 'a'}, {char : 'b'}, ...]</code>. Then in your iterator you can change elements of array through changing of the <code>char</code> property

<pre><code>let arr = [{char: 'a'}, {char :'b'}, ...];

for (let v of arr) {
 if (v.char === 'c') {
 v.char = 'f';
 break;
 } 
}
</code></pre>

blocks|key|597987|text|v不是对数组元素的引用，它只是一个变量，它被分配给数组迭代器产生的值。如果分配给它，只会更改变量v，而不会更改数组。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|597988|为此，您需要显式引用该属性及其索引，并将其赋值：|597989|let+arr+=+['a',+'b',+'c',+'d',+'e'];
for+(let+[i,+v]+of+arr.entries())+{
++++if+(v+===+'c')++{
++++++arr[i]+=+'f';
++++++break;
++++}+++++++
}
console.log(arr);+//+['a',+'b',+'f',+'d',+'e']|code-block|syntax|javascript|597990|迭代器不提供一种改变底层结构的方法，您需要自己去做。|597991|entityMap^0|0|1|1C|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|X|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

<code>v</code> is not a reference to the array element, it's just a variable that is assigned the value that the array iterator yields. If you assign to it, only the variable <code>v</code> changes but not the array.

To do that, you need to explicitly reference the property with its index and assign to it:

<pre><code>let arr = ['a', 'b', 'c', 'd', 'e'];
for (let [i, v] of arr.entries()) {
 if (v === 'c') {
 arr[i] = 'f';
 break;
 } 
}
console.log(arr); // ['a', 'b', 'f', 'd', 'e']
</code></pre>

An iterator does not provide a way to mutate the underlying structure, you need to do it yourself.

blocks|key|598017|text|在同时更改v之前，数组和v指向--或者在本例中--具有相同的值：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|598018|arr[2]+->+'c'+<-+v|code-block|syntax|javascript|598019|更改v后，它具有不同的值，但没有更改数组：|598020|arr[2]+->+'c'++v+->+'f'|598021|v和arr[2]只是占位符，但不同的占位符。|598022|entityMap^0|5|1|C|1|0|0|2|1|0|0|0|1|2|6|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|R|$]]

Before you change <code>v</code> both, the array and <code>v</code> point to - or in this case have - the same value:

<pre><code>arr[2] -&gt; 'c' &lt;- v
</code></pre>

After you change <code>v</code> it has a different value, but you didn't change the array:

<pre><code>arr[2] -&gt; 'c' v -&gt; 'f'
</code></pre>

<code>v</code> and <code>arr[2]</code> are only placeholders, but different ones.

blocks|key|2625319|text|正确的答案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2625320|let+arr+=+['a',+'b',+'c',+'d',+'e'];

let+i+=+0;
for+(let+v+of+arr)+{
++if+(v+==+'c')++{
++++arr[i]+=+'f';
++++break;
++}
++i%2B%2B;
}
console.log(arr);|code-block|syntax|javascript|2625321|-P|2625322|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

The correct answer:

<pre><code>let arr = ['a', 'b', 'c', 'd', 'e'];

let i = 0;
for (let v of arr) {
 if (v == 'c') {
 arr[i] = 'f';
 break;
 }
 i++;
}
console.log(arr);
</code></pre>

:-P

How to I change the object in the array with For-of loop?
Following code:

<pre><code>let arr = ['a', 'b', 'c', 'd', 'e'];

for (let v of arr) {
 if (v === 'c') {
 v = 'f';
 break;
 } 
}

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

I want to find the first letter c and change it to an f, but arr doesn't get changed, probably because it is not referenced ? But shouldn't the v of arr make that the object v is the same as the one in arr ?

How to change an element in for-of loop

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。

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如何用For-of循环更改数组中的对象？以下代码：let arr = ['a', 'b', 'c', 'd', 'e'];for (let v of arr) {    if (v === 'c')  {      v = 'f';      break;    }       }console.log(arr);我想...

问如何在for-of循环中更改元素
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