blocks|key|2998000|text|Never+loop+over+an+array+with+for...in.|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2998001|2998002|以任意顺序遍历对象的可枚举属性。|blockquote|style|BOLD|2998003|2998004|2998005|Why+is+using+"for...in"+with+array+iteration+a+bad+idea?|2998006|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Statements/for...in|1|https://stackoverflow.com/questions/500504/javascript-for-in-with-arrays^0|0|13|0|0|0|7|2|0|0|0|0|1K|1|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@$A|Y|B|Z|1|10]]|C|$]]|$1|D|3|-4|5|6|7|11|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|12|8|@$A|13|B|14|H|I]]|9|@]|C|$]]|$1|J|3|-4|5|6|7|15|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|16|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|N|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|O|$P|$5|Q|R|S|C|$T|U]]|V|$5|Q|R|S|C|$T|W]]]]

<a href="https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Statements/for...in" rel="nofollow noreferrer">Never loop over an array with for...in.</a>

<blockquote>
 Iterates over the enumerable properties of an object, in arbitrary order.
</blockquote>

<a href="https://stackoverflow.com/questions/500504/javascript-for-in-with-arrays">Why is using &quot;for...in&quot; with array iteration a bad idea?</a>

blocks|key|3482085|text|正如jbabey所说，在Javascript中使用for+..+in循环是危险和不确定的(随机顺序--有时)。在解析关联数组中的对象时，最常用的就是它。但是，如果您坚持保留for+..+in，请使用if块包装for的内部，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3482086|for+(var+i+in+aLines)
{
++++if(aLines.hasOwnProperty(i))
++++{
++++++++//+...+Do+stuff+here
++++}
}|code-block|syntax|javascript|3482087|否则，只需将其更改为经典的增量for循环即可消除该错误：|3482088|for+(var+i+=+0;+i+<+aLines.length;+i%2B%2B)
{
+++if+(+!aLines[i]+)+{+alert(+"Error!"+);+continue;+}
+++alert(+i+%2B+":+\""+%2B+aLines[i]++%2B+"\""+);
}|3482089|entityMap^0|P|9|2E|9|2R|2|2W|3|0|0|F|3|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|P|$]]

As jbabey said, using <code>for .. in</code> loops in Javascript is risky and undeterministic (random order--sometimes). You would most commonly use that for parsing through objects in associative arrays.
But, if you insist on keeping the <code>for .. in</code>, wrap the inside of the <code>for</code> with an <code>if</code> block like such:

<pre><code>for (var i in aLines)
{
 if(aLines.hasOwnProperty(i))
 {
 // ... Do stuff here
 }
}
</code></pre>

Otherwise, just change it to a classic incremental <code>for</code> loop to get rid of that error:

<pre><code>for (var i = 0; i &lt; aLines.length; i++)
{
 if ( !aLines[i] ) { alert( "Error!" ); continue; }
 alert( i + ": \"" + aLines[i] + "\"" );
}
</code></pre>

blocks|key|2998069|text|您应该对数组使用常规的for循环，因为for-in还将返回Array对象中的所有其他属性键。这就是为什么你会看到"hasObject“(在我的浏览器中，我看到了更多)：因为你的数组有函数"hasObject"，所以当你枚举所有数组的属性时，就会出现这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2998070|正确的for循环：|2998071|++for+(+var+i+=+0,+ii+=+aLines.length;+i<ii;+i%2B%2B+)
++{
++++if+(+!aLines[i]+)+{+alert(+"Error!"+);+continue;+}
++++alert(+i+%2B+":+\""+%2B+aLines[i]++%2B+"\""+);
++}|code-block|syntax|javascript|2998072|下面是将for-in循环替换为for循环的代码，它按预期工作：|2998073|http://jsfiddle.net/SamFent/4rzTh/|offset|length|2998074|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|0|0|Y|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]]|$1|I|3|J|5|6|7|Y|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|Z|8|@]|9|@$M|10|N|11|1|12]]|A|$]]|$1|O|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|L]]]]

You should use a regular for loop for arrays, because for-in will also return all the other property keys in the Array object. This is why you are seeing "hasObject" (and in my browser, I see a lot more after that): because your array has the function "hasObject", so when you enumerate all of Array's properties this comes up.

The correct for-loop:

<pre><code> for ( var i = 0, ii = aLines.length; i&lt;ii; i++ )
 {
 if ( !aLines[i] ) { alert( "Error!" ); continue; }
 alert( i + ": \"" + aLines[i] + "\"" );
 }
</code></pre>

Here is your code with the for-in loop replaced with a for loop, and it works as expected:

<a href="http://jsfiddle.net/SamFent/4rzTh/" rel="nofollow">http://jsfiddle.net/SamFent/4rzTh/</a>

blocks|key|2998147|text|您最终得到的是Error!，因为拆分得到的是空行""，而当您使用if(!aLines[i])检查它时，它会返回true，因为它是空/null/nothing。你可以在fiddle中检查它，你从end中删除空行，它不会遍历数组4次。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2998148|我还添加了以下代码来显示警报：|2998149|++++var+a="";
++++if(!a){
++++++++alert("!a");
++++}|code-block|syntax|javascript|2998150|entityMap|0|LINK|mutability|MUTABLE|url|http://jsfiddle.net/amantur/NB3n7/^0|7|6|O|2|W|E|1J|4|2B|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|17|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

You are getting <code>Error!</code> in end because the splitting is giving you empty line <code>""</code> and when you check for it with <code>if(!aLines[i])</code> it returns <code>true</code> because it is empty/null/nothing. You can check it here in a <a href="http://jsfiddle.net/amantur/NB3n7/" rel="nofollow">fiddle</a>, you remove the empty line from end and it does not go over array 4 times.

I have also put in following code which shows alert:

<pre><code> var a="";
 if(!a){
 alert("!a");
 }
</code></pre>

I pass in an array of error messages to parse. An example input would be:

<pre><code>"An item with this x Id already exists.
 An item with this y id already exists.
 An item with this barcode already exists.
"
</code></pre>

That is, the string is literally each line above separated by a \n, with a final \n at the end.

<pre><code>function( msg )
{
 alert( "\"" + msg + "\"" );
 var aLines = msg.split( /\r?\n+/ );

 for ( var i in aLines )
 {
 if ( !aLines[i] ) { alert( "Error!" ); continue; }
 alert( i + ": \"" + aLines[i] + "\"" );
 }
}
</code></pre>

I split it into lines, and iterate over the lines. At index 3 there is no line and the first conditional triggers. Should that not be an empty line? e.g. ""

Then the loop actually goes one more element to 4, and shows a the contents of a function.

That is I get - five alerts:

<pre><code>0: "An item with this x Id already exists."
1: "An item with this y id already exists."
2: "An item with this barcode already exists."
Error!
</code></pre>

The last one is most bizarre:

<pre><code>hasObject: "function(o) {
 var l = this.length + 1;
 ... more lines ...
}
</code></pre>

I don't understand what is happening here. Why is it iterating over one more element? And why is the last element a function? And shouldn't offset 3 be an empty string? That is I should not be alerting "Error!" here.

Iterating over array of strings produces error

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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我传入一个要解析的错误消息数组。一个输入示例是："An item with this x Id already exists. An item with this y id already exists. An item with this barcode already exists."也就是说，字符串实际上是上面的...

问迭代字符串数组会产生错误
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