blocks|key|668224|text|您可以尝试如下所示来测试和修剪长度：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668225|http://jsfiddle.net/orolo/wJDXL/|offset|length|668226|​|668227|var+longArray+=+[1,+2,+3,+4,+5,+6,+7,+8];

if+(longArray.length+>=+6)+{
++longArray.length+=+3;
}

alert(longArray);+//1,+2,+3|code-block|syntax|javascript|668228|668229|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|W|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|G|5|6|7|11|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|C]]]]

You could try something like this to test and trim the length:

<a href="http://jsfiddle.net/orolo/wJDXL/" rel="nofollow noreferrer">http://jsfiddle.net/orolo/wJDXL/</a>

<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 longArray = [1, 2, 3, 4, 5, 6, 7, 8];

if (longArray.length &gt;= 6) {
 longArray.length = 3;
}

alert(longArray); //1, 2, 3</code></pre>
</div>
</div>

blocks|key|668271|text|它将非常依赖于浏览器。100个项目听起来不是一个很大的数字--我希望你能比这个数字高得多。几千个应该不是问题。可能存在的问题是总内存消耗。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668272|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It will be very browser dependant. 100 items doesn't sound like a large number - I expect you could go a lot higher than that. Thousands shouldn't be a problem. What may be a problem is the total memory consumption.

blocks|key|668344|text|我厚颜无耻地在内存中拉取了一些相当大的数据集，尽管它确实变得很慢，但它花费了大约15个月的数据，并在数据集上进行了相当密集的计算。我怀疑您会遇到内存问题，除非您对数据和许多行进行了密集的计算。使用不同的模拟结果集进行性能分析和基准测试将是评估性能的最佳选择。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668345|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I have shamelessly pulled some pretty big datasets in memory, and altough it did get sluggish it took maybe 15 Mo of data upwards with pretty intense calculations on the dataset. I doubt you will run into problems with memory unless you have intense calculations on the data and many many rows. Profiling and benchmarking with different mock resultsets will be your best bet to evaluate performance.

blocks|key|885582|text|我已经构建了一个性能框架，可以操作数百万个数据集并绘制图形，即使这样，javascript的计算延迟也只有几十毫秒。除非您担心超过数组大小限制，否则我认为您没有太多需要担心的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|885583|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I have built a performance framework that manipulates and graphs millions of datasets, and even then, the javascript calculation latency was on order of tens of milliseconds. Unless you're worried about going over the array size limit, I don't think you have much to worry about.

blocks|key|668460|text|无需修剪数组，只需将其作为循环缓冲区进行寻址(索引%25+maxlen)。这将确保它永远不会超过限制(实现循环缓冲区意味着一旦到达末尾，您就会再次回到开头-不可能溢出数组的末尾)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668461|例如：|668462|var+container+=+new+Array+();
var+maxlen+=+100;
var+index+=+0;

//+'store'+1538+items+(only+the+last+'maxlen'+items+are+kept)
for+(var+i=0;+i<1538;+i%2B%2B)+{
+++container+[index%2B%2B+%25+maxlen]+=+"storing"+%2B+i;
}

//+get+element+at+index+11+(you+want+the+11th+item+in+the+array)
eleventh+=+container+[(index+%2B+11)+%25+maxlen];

//+get+element+at+index+11+(you+want+the+11th+item+in+the+array)
thirtyfifth+=+container+[(index+%2B+35)+%25+maxlen];

//+print+out+all+100+elements+that+we+have+left+in+the+array,+note
//+that+it+doesn't+matter+if+we+address+past+100+-+circular+buffer
//+so+we'll+simply+get+back+to+the+beginning+if+we+do+that.
for+(i=0;+i<200;+i%2B%2B)+{
+++document.write+(container[(index+%2B+i)+%25+maxlen]+%2B+" \n");
}|code-block|syntax|javascript|668463|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|$]]

No need to trim the array, simply address it as a circular buffer (index % maxlen). This will ensure it never goes over the limit (implementing a circular buffer means that once you get to the end you wrap around to the beginning again - not possible to overrun the end of the array).

For example:

<pre><code>var container = new Array ();
var maxlen = 100;
var index = 0;

// 'store' 1538 items (only the last 'maxlen' items are kept)
for (var i=0; i&lt;1538; i++) {
 container [index++ % maxlen] = "storing" + i;
}

// get element at index 11 (you want the 11th item in the array)
eleventh = container [(index + 11) % maxlen];

// get element at index 11 (you want the 11th item in the array)
thirtyfifth = container [(index + 35) % maxlen];

// print out all 100 elements that we have left in the array, note
// that it doesn't matter if we address past 100 - circular buffer
// so we'll simply get back to the beginning if we do that.
for (i=0; i&lt;200; i++) {
 document.write (container[(index + i) % maxlen] + "&lt;br&gt;\n");
}
</code></pre>

Context: I'm building a little site that reads an rss feed, and updates/checks the feed in the background. I have one array to store data to display, and another which stores ID's of records that have been shown.

Question: How many items can an array hold in Javascript before things start getting slow, or sluggish. I'm not sorting the array, but am using jQuery's inArray function to do a comparison.

The website will be left running, and updating and its unlikely that the browser will be restarted / refreshed that often.

If I should think about clearing some records from the array, what is the best way to remove some records after a limit, like 100 items.

Maximum size of an Array in Javascript

上下文:我正在构建一个小站点，它可以读取rss提要，并在后台更新/检查提要。我有一个数组用于存储要显示的数据，另一个数组用于存储已显示的记录的ID。问:在开始变慢或变慢之前，一个数组可以在Javascript中容纳多少项。我不是对数组进行排序，而是使用jQuery的inArray函数进行比较。网站将保持运行和更新，浏览...

问Javascript中数组的最大大小
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