blocks|key|4439964|text|我相信你要找的是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4439965|//+...inside+the+render()+function

var+size+=+3;
var+items+=+list.slice(0,+size).map(i+=>+{
++++return+<myview+item={i}+key={i.id}+/>
}

return+(
++<div>
++++{items}
++</div>+++
)|code-block|syntax|javascript|4439966|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I believe what you're looking for is: 

<pre><code>// ...inside the render() function

var size = 3;
var items = list.slice(0, size).map(i =&gt; {
 return &lt;myview item={i} key={i.id} /&gt;
}

return (
 &lt;div&gt;
 {items}
 &lt;/div&gt; 
)
</code></pre>

blocks|key|4439912|text|要获取数组的第一个n元素，请使用|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4439913|const+slicedArray+=+array.slice(0,+n);|code-block|syntax|javascript|4439914|entityMap^0|9|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

To get the first <code>n</code> elements of an array, use
<pre><code>const slicedArray = array.slice(0, n);
</code></pre>

blocks|key|4440101|text|arr.length+=+n|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4440102|这可能令人惊讶，但数组的length属性不仅用于获取数组元素的数量，而且还是可写的，可用于设置数组的长度MDN+link。这将使数组发生变化。|unstyled|offset|length|style|CODE|4440103|如果你不关心不变性，或者不想分配内存，比如对于游戏，这将是最快的方法。|4440104|清空数组|4440105|arr.length+=+0|4440106|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length^0|0|C|6|1G|8|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|Z|8|@$G|10|H|11|I|J]]|9|@$G|12|H|13|1|14]]|A|$]]|$1|K|3|L|5|F|7|15|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|16|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|17|8|@]|9|@]|A|$B|C]]|$1|Q|3|-4|5|F|7|18|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

<pre><code>arr.length = n
</code></pre>
This might be surprising but <code>length</code> property of an array is not only used to get number of array elements but it's also writable and can be used to set array's length <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length" rel="noreferrer">MDN link</a>. This will mutate the array.
If you don't care about immutability or don't want to allocate memory i.e. for a game this will be the fastest way.
to empty an array
<pre><code>arr.length = 0
</code></pre>

blocks|key|4440041|text|您可以使用数组的index进行过滤。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4440042|​|4440043|var+months+=+['Jan',+'March',+'April',+'June'];
months+=+months.filter((month,idx)+=>+idx+<+2)
console.log(months);|code-block|syntax|javascript|4440044|4440045|entityMap^0|8|5|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|T|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|U|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|O|$]]

You can filter using <code>index</code> of array. 

<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>var months = ['Jan', 'March', 'April', 'June'];
months = months.filter((month,idx) =&gt; idx &lt; 2)
console.log(months);</code></pre>
</div>
</div>

blocks|key|4440041|text|不要试图使用map函数来执行此操作。应使用Map函数将值从一个事物映射到另一个事物。当输入和输出的数量匹配时。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4440042|在这种情况下，使用filter函数，该函数在数组上也可用。当您想要有选择地获取符合特定条件的值时，可以使用Filter函数。然后，您可以像这样编写您的代码|4440043|var+items+=+list
+++++++++++++.filter((i,+index)+=>+(index+<+3))
+++++++++++++.map((i,+index)+=>+{
+++++++++++++++++++return+(
+++++++++++++++++++++<myview+item={i}+key={i.id}+/>
+++++++++++++++++++);
++++++++++++++});|code-block|syntax|javascript|4440044|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Do not try doing that using a map function. Map function should be used to map values from one thing to other. When the number of input and output match.

In this case use filter function which is also available on the array. Filter function is used when you want to selectively take values maching certain criteria. Then you can write your code like

<pre><code>var items = list
 .filter((i, index) =&gt; (index &lt; 3))
 .map((i, index) =&gt; {
 return (
 &lt;myview item={i} key={i.id} /&gt;
 );
 });
</code></pre>

blocks|key|4440134|text|下面的方法对我很有效。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4440135|array.slice(+where_to_start_deleting,+array.length+)|code-block|syntax|javascript|4440136|下面是一个例子|4440137|var+fruits+=+["Banana",+"Orange",+"Apple",+"Mango"];
fruits.slice(2,+fruits.length);
//Banana,Orange++->These+first+two+we+get+as+resultant|4440138|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The following worked for me.

<pre><code>array.slice( where_to_start_deleting, array.length )
</code></pre>

Here is an example

<pre><code>var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.slice(2, fruits.length);
//Banana,Orange -&gt;These first two we get as resultant
</code></pre>

blocks|key|4440098|text|使用lodash，take函数，您可以通过以下方式来实现：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4440099|_.take([1,+2,+3]);
//+=>+[1]
+
_.take([1,+2,+3],+2);
//+=>+[1,+2]
+
_.take([1,+2,+3],+5);
//+=>+[1,+2,+3]
+
_.take([1,+2,+3],+0);
//+=>+[]|code-block|syntax|javascript|4440100|entityMap|0|LINK|mutability|MUTABLE|url|https://lodash.com/docs/4.17.15#take^0|9|4|2|6|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

With <a href="https://lodash.com/docs/4.17.15#take" rel="noreferrer">lodash</a>, <code>take</code> function, you can achieve this by following:
<pre><code>_.take([1, 2, 3]);
// =&gt; [1]
 
_.take([1, 2, 3], 2);
// =&gt; [1, 2]
 
_.take([1, 2, 3], 5);
// =&gt; [1, 2, 3]
 
_.take([1, 2, 3], 0);
// =&gt; []
</code></pre>

blocks|key|4440129|text|试着这样从list中获取第一个n元素：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4440130|const+slicedList+=+list.slice(0,+n);|code-block|syntax|javascript|4440131|示例：|4440132|const+list+=+[1,2,3,4,5]
console.log(list.slice(0,+3))+//+Should+return+[1,2,3]+
console.log(list.slice(0,+10))+//+Returns+[1,2,3,4,5]+since+this+is+all+we+have+in+1st+10+elements|4440133|​|4440134|entityMap^0|F|1|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|Y|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

Just try this to get first <code>n</code> elements from list:
<pre><code>const slicedList = list.slice(0, n);
</code></pre>
Example:
<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 list = [1,2,3,4,5]
console.log(list.slice(0, 3)) // Should return [1,2,3] 
console.log(list.slice(0, 10)) // Returns [1,2,3,4,5] since this is all we have in 1st 10 elements</code></pre>
</div>
</div>

blocks|key|4440318|text|slice()方法将数组一部分的浅表副本返回到从头到尾(不包括end+)选择的新数组对象中，其中start和end表示该数组中项的索引。原始数组不会被修改。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4440319|const+animals+=+['ant',+'bison',+'camel',+'duck',+'elephant'];

console.log(animals.slice(2));
//+expected+output:+Array+["camel",+"duck",+"elephant"]

console.log(animals.slice(2,+4));
//+expected+output:+Array+["camel",+"duck"]

console.log(animals.slice(1,+5));
//+expected+output:+Array+["bison",+"camel",+"duck",+"elephant"]

console.log(animals.slice(-2));
//+expected+output:+Array+["duck",+"elephant"]

console.log(animals.slice(2,+-1));
//+expected+output:+Array+["camel",+"duck"]|code-block|syntax|javascript|4440320|know+more|offset|length|4440321|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice^0|0|0|0|9|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

The slice() method returns a shallow copy of a portion of an array into a new array object selected from start to end (end not included) where start and end represent the index of items in that array. The original array will not be modified.
<pre><code>const animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];

console.log(animals.slice(2));
// expected output: Array [&quot;camel&quot;, &quot;duck&quot;, &quot;elephant&quot;]

console.log(animals.slice(2, 4));
// expected output: Array [&quot;camel&quot;, &quot;duck&quot;]

console.log(animals.slice(1, 5));
// expected output: Array [&quot;bison&quot;, &quot;camel&quot;, &quot;duck&quot;, &quot;elephant&quot;]

console.log(animals.slice(-2));
// expected output: Array [&quot;duck&quot;, &quot;elephant&quot;]

console.log(animals.slice(2, -1));
// expected output: Array [&quot;camel&quot;, &quot;duck&quot;]
</code></pre>
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice" rel="nofollow noreferrer">know more</a>

blocks|key|4440264|text|Pawel的答案似乎是在资源关键型环境中的最佳选择，当剩余的元素可以被丢弃时。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4440265|考虑到数组已经更小的情况，这是一个小小的改进：|4440266|if+(arr.length+>+n)+arr.length+=+n|offset|length|style|CODE|4440267|entityMap^0|0|0|0|Y|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@$F|O|G|P|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

Pawel's answer seems the best option in resource-critical environments, and when the remaining elements can be discarded.
Considering the case when the array is already smaller, this is a little improvement:
<code>if (arr.length &gt; n) arr.length = n</code>

blocks|key|4440286|text|虽然这个问题很老了，但对于2021年，有一个完整的LINQ+to+object实现，它是用ECMAScript+(javascript)的最新功能编写的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4440287|Github存储库是：https://github.com/IlanAmoyal/WebPartyLinq|offset|length|4440288|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/IlanAmoyal/WebPartyLinq^0|0|B|16|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Although this question is very old, as for 2021, there is a full implementation of LINQ to object written with the latest feature of ECMAScript (javascript).
The Github repository is: <a href="https://github.com/IlanAmoyal/WebPartyLinq" rel="nofollow noreferrer">https://github.com/IlanAmoyal/WebPartyLinq</a>

I am working with Javascript(ES6) /FaceBook react and trying to get the first 3 elements of an array that varies in size. I would like do the equivalent of Linq take(n).

In my Jsx file I have the following:

<pre><code>var items = list.map(i =&gt; {
 return (
 &lt;myview item={i} key={i.id} /&gt;
 );
});
</code></pre>

Then to get the first 3 items I tried

<pre><code> var map = new Map(list);
 map.size = 3;
 var items = map(i =&gt; {
 return (&lt;SpotlightLandingGlobalInboxItem item={i} key={i.id} /&gt;);
 });
</code></pre>

This didn't work as map doesn't have a set function.

Can you please help?

How to get first N number of elements from an array

我正在使用Javascript(ES6) /FaceBook react，并试图获得大小不同的数组的前3个元素。我想做一个等价于Linq take(n)的函数。在我的Jsx文件中，我有以下内容：var items = list.map(i => { return ( <myview item={i} key={i.id} /> );});然后，为了得到我尝试的前3个项目 var map

问如何从数组中获取前N个元素
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回答 11

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问如何从数组中获取前N个元素
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