blocks|key|4479648|text|ECMAScript的JavaScript实现可以因浏览器而异，但是对于Chrome，有许多字符串操作(substr、slice、regex等)。只需保留对原始字符串的引用，而不是复制字符串。这是Chrome+(Bug+#2869)中的一个已知问题。要强制复制字符串，请使用以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4479649|var+string_copy+=+('+'+%2B+original_string).slice(1);|code-block|syntax|javascript|4479650|此代码的工作方式是在字符串的前面附加一个空格。在Chrome的实现中，这种连接会产生一个字符串副本。则可以引用空格之后的子串。|4479651|解决方案的这个问题已在此处重新创建：http://jsfiddle.net/ouvv4kbs/1/|4479652|警告:加载需要很长时间，请打开Chrome调试控制台查看进度打印输出。|4479653|//+We+would+expect+this+program+to+use+~1+MB+of+memory,+however+taking
//+a+Heap+Snapshot+will+show+that+this+program+uses+~100+MB+of+memory.
//+If+the+processed+data+size+is+increased+to+~1+GB,+the+Chrome+tab
//+will+crash+due+to+running+out+of+memory.

function+randomString(length)+{
++var+alphabet+=+'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
++var+result+=+'';
++for+(var+i+=+0;+i+<+length;+i%2B%2B)+{
++++result+%2B=
++++++++alphabet[Math.round(Math.random()+*+(alphabet.length+-+1))];
++}
++return+result;
};

var+substrings+=+[];
var+extractSubstring+=+function(huge_string)+{
++var+substring+=+huge_string.substr(0,+100+*+1000+/*+100+KB+*/);
++//+Uncommenting+this+line+will+force+a+copy+of+the+string+and+allow
++//+the+unused+memory+to+be+garbage+collected
++//+substring+=+('+'+%2B+substring).slice(1);
++substrings.push(substring);
};

//+Process+100+MB+of+data,+but+only+keep+1+MB.
for+(var+i+=++0;+i+<+10;+i%2B%2B)+{
++console.log(10+*+(i+%2B+1)+%2B+'MB+processed');
++var+huge_string+=+randomString(10+*+1000+*+1000+/*+10+MB+*/);
++extractSubstring(huge_string);
}

//+Do+something+which+will+keep+a+reference+to+substrings+around+and
//+prevent+it+from+being+garbage+collected.
setInterval(function()+{
++var+i+=+Math.round(Math.random()+*+(substrings.length+-+1));
++document.body.innerHTML+=+substrings[i].substr(0,+10);
},+2000);|4479654|​|4479655|📷|atomic|4479656|4479657|entityMap|0|LINK|mutability|MUTABLE|url|https://code.google.com/p/v8/issues/detail?id=2869|1|http://jsfiddle.net/ouvv4kbs/1/|2|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/5cec0958668cee024c9ce266c3aeb0de.png|imageAlt^0|2Y|9|0|0|0|0|I|V|1|0|0|0|0|0|1|2|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@$A|1D|B|1E|1|1F]]|C|$]]|$1|D|3|E|5|F|7|1G|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1H|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|1I|8|@]|9|@$A|1J|B|1K|1|1L]]|C|$]]|$1|M|3|N|5|6|7|1M|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1N|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|1O|8|@]|9|@]|C|$]]|$1|S|3|T|5|U|7|1P|8|@]|9|@$A|1Q|B|1R|1|1S]]|C|$]]|$1|V|3|R|5|6|7|1T|8|@]|9|@]|C|$]]|$1|W|3|-4|5|6|7|1U|8|@]|9|@]|C|$]]]|X|$Y|$5|Z|10|11|C|$12|13]]|14|$5|Z|10|11|C|$12|15]]|16|$5|17|10|18|C|$19|1A|1B|-4]]]]

JavaScript's implementation of ECMAScript can vary from browser to browser, however for Chrome, many string operations (substr, slice, regex, etc.) simply retain references to the original string rather than making copies of the string. This is a known issue in Chrome (<a href="https://code.google.com/p/v8/issues/detail?id=2869" rel="noreferrer" title="Bug #2869">Bug #2869</a>). To force a copy of the string, the following code works:

<pre><code>var string_copy = (' ' + original_string).slice(1);
</code></pre>

This code works by appending a space to the front of the string. This concatenation results in a string copy in Chrome's implementation. Then the substring after the space can be referenced.

This problem with the solution has been recreated here: <a href="http://jsfiddle.net/ouvv4kbs/1/" rel="noreferrer">http://jsfiddle.net/ouvv4kbs/1/</a> 

WARNING: takes a long time to load, open Chrome debug console to see a progress printout.

<pre><code>// We would expect this program to use ~1 MB of memory, however taking
// a Heap Snapshot will show that this program uses ~100 MB of memory.
// If the processed data size is increased to ~1 GB, the Chrome tab
// will crash due to running out of memory.

function randomString(length) {
 var alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
 var result = '';
 for (var i = 0; i &lt; length; i++) {
 result +=
 alphabet[Math.round(Math.random() * (alphabet.length - 1))];
 }
 return result;
};

var substrings = [];
var extractSubstring = function(huge_string) {
 var substring = huge_string.substr(0, 100 * 1000 /* 100 KB */);
 // Uncommenting this line will force a copy of the string and allow
 // the unused memory to be garbage collected
 // substring = (' ' + substring).slice(1);
 substrings.push(substring);
};

// Process 100 MB of data, but only keep 1 MB.
for (var i = 0; i &lt; 10; i++) {
 console.log(10 * (i + 1) + 'MB processed');
 var huge_string = randomString(10 * 1000 * 1000 /* 10 MB */);
 extractSubstring(huge_string);
}

// Do something which will keep a reference to substrings around and
// prevent it from being garbage collected.
setInterval(function() {
 var i = Math.round(Math.random() * (substrings.length - 1));
 document.body.innerHTML = substrings[i].substr(0, 10);
}, 2000);
</code></pre>

<a href="https://i.stack.imgur.com/obsf1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/obsf1.png" alt="enter image description here"></a>

blocks|key|4479710|text|我对字符串、对象、数组等使用Object.assign()方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4479711|const+newStr+=+Object.assign("",+myStr);
const+newObj+=+Object.assign({},+myObj);
const+newArr+=+Object.assign([],+myArr);|code-block|syntax|javascript|4479712|请注意，Object.assign仅复制对象内的键及其属性值(仅一级)。有关深度克隆嵌套对象的信息，请参考以下示例：|4479713|let+obj100+=+{+a:0,+b:{+c:0+}+};
let+obj200+=+JSON.parse(JSON.stringify(obj100));
obj100.a+=+99;+obj100.b.c+=+99;+//+No+effect+on+obj200|4479714|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign^0|E|F|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

I use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign" rel="nofollow noreferrer">Object.assign()</a> method for string, object, array, etc:
<pre><code>const newStr = Object.assign(&quot;&quot;, myStr);
const newObj = Object.assign({}, myObj);
const newArr = Object.assign([], myArr);
</code></pre>
Note that Object.assign only copies the keys and their properties values inside an object (one-level only). For deep cloning a nested object, refer to the following example:
<pre><code>let obj100 = { a:0, b:{ c:0 } };
let obj200 = JSON.parse(JSON.stringify(obj100));
obj100.a = 99; obj100.b.c = 99; // No effect on obj200
</code></pre>

blocks|key|4479769|text|当我推入数组时，我遇到了一个问题。每个条目都会以相同的字符串结束，因为它引用了一个对象上的值，这个值在我通过.next()函数迭代结果时发生了变化。下面是允许我复制字符串并在数组结果中获得唯一值的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4479770|while+(results.next())+{
++var+locationName+=+String(results.name);
++myArray.push(locationName);
}|code-block|syntax|javascript|4479771|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 was getting an issue when pushing into an array. Every entry would end up as the same string because it was referencing a value on an object that changed as I iterated over results via a .next() function. Here is what allowed me to copy the string and get unique values in my array results:

<pre><code>while (results.next()) {
 var locationName = String(results.name);
 myArray.push(locationName);
}
</code></pre>

blocks|key|4480651|text|您可以使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4480652|+String.prototype.repeat(1)+|code-block|syntax|javascript|4480653|它似乎工作得很好。请参阅MDN+documentation+on+repeat。|offset|length|style|CODE|4480654|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat^0|0|0|X|6|C|R|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

You can use:

<pre><code> String.prototype.repeat(1) 
</code></pre>

It seems to work well. Refer the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat" rel="noreferrer">MDN documentation on <code>repeat</code></a>.

blocks|key|4479830|text|不确定如何测试，但使用字符串插值来创建新的字符串变量是否有效？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4479831|newString+=+`${oldString}`|code-block|syntax|javascript|4479832|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|$]]

not sure how to test, but does using string interpolation to create a new string variable work?

<pre><code>newString = `${oldString}`
</code></pre>

blocks|key|4479894|text|我通常使用strCopy+=+new+String+(originalStr);，这是不是因为某些原因而不被推荐呢？|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4479895|entityMap^0|5|Z|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

I typically use <code>strCopy = new String (originalStr);</code> 
Is this not recommended for some reason?

blocks|key|4479901|text|我遇到了这个问题，我是这样处理的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4479902|let+copy_string+=+[];
copy_string.splice(0,+0,+str);|code-block|syntax|javascript|4479903|我相信这会将字符串深度复制到copy_string。|4479904|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|$]]

I have run into this problem and this was how I coped with it:
<pre><code>let copy_string = [];
copy_string.splice(0, 0, str);
</code></pre>
I believe this would deep copy str to copy_string.

blocks|key|4480809|text|使用String.slice()|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4480810|​|4480811|const+str+=+'The+quick+brown+fox+jumps+over+the+lazy+dog.';

//+creates+a+new+string+without+modifying+the+original+string
const+new_str+=+str.slice();

console.log(+new_str+);|code-block|syntax|javascript|4480812|4480813|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

using String.slice()
<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 str = 'The quick brown fox jumps over the lazy dog.';

// creates a new string without modifying the original string
const new_str = str.slice();

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

I have some javascript code which looks like this:

<pre><code>var myClass = {
 ids: {}
 myFunc: function(huge_string) {
 var id = huge_string.substr(0,2);
 ids[id] = true;
 }
}
</code></pre>

Later the function gets called with some large strings (100 MB+). I only want to save a short id which I find in each string. However, the Google Chrome's substring function (actually regex in my code) only returns a "sliced string" object, which references the original. So after a series of calls to <code>myFunc</code>, my chrome tab runs out of memory because the temporary <code>huge_string</code> objects are not able to be garbage collected.

How can I make a copy of the string <code>id</code> so that a reference to the <code>huge_string</code> is not maintained, and the <code>huge_string</code> can be garbage collected?

<a href="https://i.stack.imgur.com/pzJai.png" rel="noreferrer"><img src="https://i.stack.imgur.com/pzJai.png" alt="enter image description here"></a>

How to force JavaScript to deep copy a string?

JSON

我有一些javascript代码，看起来像这样：var myClass = {  ids: {}  myFunc: function(huge_string) {     var id = huge_string.substr(0,2);     ids[id] = true;  }}稍后，使用一些大字符串(100 M...

问如何强制JavaScript对字符串进行深度复制？
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