blocks|key|1079692|text|您需要调用hasOwnProperty函数来检查是否在对象本身(与其原型相反)上实际定义了该属性，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1079693|for+(var+key+in+widthRange)+{
++++if+(key+===+'length'+%7C%7C+!widthRange.hasOwnProperty(key))+continue;
++++var+value+=+widthRange[key];
}|code-block|syntax|javascript|1079694|请注意，您需要对length进行单独检查。|1079695|但是，您在这里根本不应该使用数组；您应该使用常规对象。所有Javascript对象都作为关联数组运行。|1079696|例如：|1079697|var+widthRange+=+{+};++//Or+new+Object()
widthRange[46]+=+{+sel:46,+min:0,++max:52+};
widthRange[66]+=+{+sel:66,+min:52,+max:70+};
widthRange[90]+=+{+sel:90,+min:70,+max:94+};|1079698|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Object/hasOwnProperty^0|5|E|5|E|0|0|0|8|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1A|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1B|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

You need to call the <a href="https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Object/hasOwnProperty" rel="noreferrer"><code>hasOwnProperty</code></a> function to check whether the property is actually defined on the object itself (as opposed to its prototype), like this:

<pre><code>for (var key in widthRange) {
 if (key === 'length' || !widthRange.hasOwnProperty(key)) continue;
 var value = widthRange[key];
}
</code></pre>

Note that you need a separate check for <code>length</code>. 
However, you shouldn't be using an array here at all; you should use a regular object. All Javascript objects function as associative arrays. 

For example:

<pre><code>var widthRange = { }; //Or new Object()
widthRange[46] = { sel:46, min:0, max:52 };
widthRange[66] = { sel:66, min:52, max:70 };
widthRange[90] = { sel:90, min:70, max:94 };
</code></pre>

blocks|key|1079725|text|您的原始示例对我来说工作得很好：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1079726|<html>
<head>
</head>
<body>
<script>
var+widthRange+=+new+Array();
widthRange[46]+=+{+sel:46,+min:0,++max:52+};
widthRange[66]+=+{+sel:66,+min:52,+max:70+};
widthRange[90]+=+{+sel:90,+min:70,+max:94+};

var+i+=+1;
for+(var+key+in+widthRange)
{
++++document.write("Key+#"+%2B+i+%2B+"+=+"+%2B+key+%2B+";+&nbsp;&nbsp;&nbsp;+min/max+=+"+%2B+widthRange[key].min+%2B+"/"+%2B+widthRange[key].max+%2B+"<br+/>");
++++i%2B%2B;
}
</script>
</html>|code-block|syntax|javascript|1079727|浏览器中的结果(+Windows+XP上的Firefox+3.6.2+)：|1079728|Key+#1+=+46;+++++min/max+=+0/52
Key+#2+=+66;+++++min/max+=+52/70
Key+#3+=+90;+++++min/max+=+70/94|1079729|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|$]]

Your original example works just fine for me:

<pre><code>&lt;html&gt;
&lt;head&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;script&gt;
var widthRange = new Array();
widthRange[46] = { sel:46, min:0, max:52 };
widthRange[66] = { sel:66, min:52, max:70 };
widthRange[90] = { sel:90, min:70, max:94 };

var i = 1;
for (var key in widthRange)
{
 document.write("Key #" + i + " = " + key + "; &amp;nbsp;&amp;nbsp;&amp;nbsp; min/max = " + widthRange[key].min + "/" + widthRange[key].max + "&lt;br /&gt;");
 i++;
}
&lt;/script&gt;
&lt;/html&gt;
</code></pre>

Results in the browser (Firefox 3.6.2 on Windows XP):

<pre><code>Key #1 = 46; min/max = 0/52
Key #2 = 66; min/max = 52/70
Key #3 = 90; min/max = 70/94
</code></pre>

blocks|key|1079734|text|看起来很管用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1079735|var+widthRange+=+new+Array();
widthRange[46]+=+{+sel:46,+min:0,++max:52+};
widthRange[66]+=+{+sel:66,+min:52,+max:70+};
widthRange[90]+=+{+sel:90,+min:70,+max:94+};

for+(var+key+in+widthRange)
{
++++document.write(widthRange[key].sel+%2B+"<br+/>");
++++document.write(widthRange[key].min+%2B+"<br+/>");
++++document.write(widthRange[key].max+%2B+"<br+/>");
}|code-block|syntax|javascript|1079736|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|$]]

Seems to work.

<pre><code>var widthRange = new Array();
widthRange[46] = { sel:46, min:0, max:52 };
widthRange[66] = { sel:66, min:52, max:70 };
widthRange[90] = { sel:90, min:70, max:94 };

for (var key in widthRange)
{
 document.write(widthRange[key].sel + "&lt;br /&gt;");
 document.write(widthRange[key].min + "&lt;br /&gt;");
 document.write(widthRange[key].max + "&lt;br /&gt;");
}
</code></pre>

blocks|key|1079777|text|我认为你应该使用一个对象({})，而不是一个数组([])。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1079778|一组数据与每个键相关联。它尖叫着使用一个对象。执行以下操作：|1079779|var+obj+=+{};
obj[46]+=+{+sel:46,+min:0,++max:52+};
obj[666]+=+{+whatever:true+};

//+This+is+what+for..in+is+for
for+(var+prop+in+obj)+{
++console.log(obj[prop]);
}|code-block|syntax|javascript|1079780|也许像这样的一些实用工具可能会有所帮助：|1079781|window.WidthRange+=+(function+()+{
++var+obj+=+{};
++return+{
++++getObj:+function+()+{return+obj;}
++++,+add:+function+(key,+data)+{
++++++++obj[key]+=+data;
++++++++return+this;+//+enabling+chaining
++++++}
++}
})();

//+Usage+(using+chaining+calls):
WidthRange.add(66,+{foo:+true})
.add(67,+{bar:+false})
.add(69,+{baz:+'maybe',+bork:'absolutely'});

var+obj+=+WidthRange.getObj();
for+(var+prop+in+obj)+{
++console.log(obj[prop]);
}|1079782|entityMap^0|D|2|P|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

I think you should use an Object (<code>{}</code>) and not an array (<code>[]</code>) for this.

A set of data is associated with each key. It screams for using an object. Do:

<pre><code>var obj = {};
obj[46] = { sel:46, min:0, max:52 };
obj[666] = { whatever:true };

// This is what for..in is for
for (var prop in obj) {
 console.log(obj[prop]);
}
</code></pre>

Maybe some utility stuff like this can help:

<pre><code>window.WidthRange = (function () {
 var obj = {};
 return {
 getObj: function () {return obj;}
 , add: function (key, data) {
 obj[key] = data;
 return this; // enabling chaining
 }
 }
})();

// Usage (using chaining calls):
WidthRange.add(66, {foo: true})
.add(67, {bar: false})
.add(69, {baz: 'maybe', bork:'absolutely'});

var obj = WidthRange.getObj();
for (var prop in obj) {
 console.log(obj[prop]);
}
</code></pre>

blocks|key|1079870|text|我写了一个函数，它可以很好地处理对象的每个实例(数组就是那些)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1079871|Object.prototype.toArray+=+function()
{
++++if(!this)
++++{
++++++return+null;
++++}

++++var+c+=+[];

++++for+(var+key+in+this)+
++++{
++++++++if+(+(+this+instanceof+Array+&&+this.constructor+===+Array+&&+key+===+'length'+)+%7C%7C+!this.hasOwnProperty(key)+)+
++++++++{
++++++++++++continue;
++++++++}

++++++++c.push(this[key]);
++++}

++++return+c;
};|code-block|syntax|javascript|1079872|用法：|1079873|var+a+++=+[+1,+2,+3+];
a[11]+++=+4;
a["js"]+=+5;

console.log(a.toArray());

var+b+=+{+one:+1,+two:+2,+three:+3,+f:+function()+{+return+4;+},+five:+5+};
b[7]+=+7;

console.log(b.toArray());|1079874|输出：|1079875|>+[+1,+2,+3,+4,+5+]
>+[+7,+1,+2,+3,+function+()+{+return+4;+},+5+]|1079876|它可能对任何人都有用。|1079877|entityMap^0|0|0|0|0|0|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

I wrote a function what works fine with every instance of Objects (Arrays are those).

<pre><code>Object.prototype.toArray = function()
{
 if(!this)
 {
 return null;
 }

 var c = [];

 for (var key in this) 
 {
 if ( ( this instanceof Array &amp;&amp; this.constructor === Array &amp;&amp; key === 'length' ) || !this.hasOwnProperty(key) ) 
 {
 continue;
 }

 c.push(this[key]);
 }

 return c;
};
</code></pre>

Usage:

<pre><code>var a = [ 1, 2, 3 ];
a[11] = 4;
a["js"] = 5;

console.log(a.toArray());

var b = { one: 1, two: 2, three: 3, f: function() { return 4; }, five: 5 };
b[7] = 7;

console.log(b.toArray());
</code></pre>

Output:

<pre><code>&gt; [ 1, 2, 3, 4, 5 ]
&gt; [ 7, 1, 2, 3, function () { return 4; }, 5 ]
</code></pre>

It may be useful for anyone.

blocks|key|1079897|text|可以使用Object.keys(array)查询字符串化的键。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1079898|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys^0|4|I|4|I|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

The stringified keys can be queried with <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys"><code>Object.keys(array)</code></a>.

blocks|key|1294898|text|...？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1294899|或者，如果您有一个要使用的项目列表...|1294900|var+range+=+[46,+66,+90]
++++,+widthRange=[]
++++,+write=[];

++++widthRange[46]+=+{+min:0,+max:52+};+
++++widthRange[66]+=+{+min:52,+max:70+};+
++++widthRange[90]+=+{+min:70,+max:94+};+

for(var+x=0;+x<range.length;+x%2B%2B){var+key,+wr;

++++key+=+range[x];

++++wr+=+widthRange[key]+%7C%7C+false;

++++if(wr===false){continue;}

++++write.push(['key:+#',key,+',+min:+',+wr.min,+'max:',+wr.max].join(''));

++++}|code-block|syntax|javascript|1294901|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|$]]

... ????

Alternatively, if you have a list of items you want to use...

<pre><code>var range = [46, 66, 90]
 , widthRange=[]
 , write=[];

 widthRange[46] = { min:0, max:52 }; 
 widthRange[66] = { min:52, max:70 }; 
 widthRange[90] = { min:70, max:94 }; 

for(var x=0; x&lt;range.length; x++){var key, wr;

 key = range[x];

 wr = widthRange[key] || false;

 if(wr===false){continue;}

 write.push(['key: #',key, ', min: ', wr.min, 'max:', wr.max].join(''));

 }
</code></pre>

blocks|key|1294921|text|假设您的数组看起来像arr+=+[+{+a:+1,+b:+2,+c:+3+},+{+a:+4,+b:+5,+c:+6+},+{+a:+7,+b:+8,+c:+9+}+]+(或者可能是其他键)，您可以这样做|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1294922|arr.map((o)+=>+{
++++return+Object.keys(o)
}).reduce((prev,+curr)+=>+{
++++return+prev.concat(curr)
}).filter((col,+i,+array)+=>+{
++++return+array.indexOf(col)+===+i
});|code-block|syntax|javascript|1294923|["a",+"b",+"c"]|1294924|entityMap^0|A|22|0|0|0|F|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Say your array looked like
<code>arr = [ { a: 1, b: 2, c: 3 }, { a: 4, b: 5, c: 6 }, { a: 7, b: 8, c: 9 } ]</code> (or possibly other keys) you could do

<pre><code>arr.map((o) =&gt; {
 return Object.keys(o)
}).reduce((prev, curr) =&gt; {
 return prev.concat(curr)
}).filter((col, i, array) =&gt; {
 return array.indexOf(col) === i
});
</code></pre>

<code>["a", "b", "c"]</code>

blocks|key|1294936|text|widthRange.map(function(_,+i)+{+return+i+});|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1294937|或|unstyled|1294938|widthRange.map((_,+i)+=>+i);|1294939|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>widthRange.map(function(_, i) { return i });
</code></pre>

or

<pre><code>widthRange.map((_, i) =&gt; i);
</code></pre>

blocks|key|1080002|text|对于您的输入数据：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1080003|let+widthRange+=+new+Array()
widthRange[46]+=+{+min:0,++max:52+}
widthRange[61]+=+{+min:52,+max:70+}
widthRange[62]+=+{+min:52,+max:70+}
widthRange[63]+=+{+min:52,+max:70+}
widthRange[66]+=+{+min:52,+max:70+}
widthRange[90]+=+{+min:70,+max:94+}|code-block|syntax|javascript|1080004|声明性方法：|1080005|const+relevantKeys+=+[46,66,90]
const+relevantValues+=+Object.keys(widthRange)
++++.filter(index+=>+relevantKeys.includes(parseInt(index)))
++++.map(relevantIndex+=>+widthRange[relevantIndex])|1080006|使用parseInt将密钥转换为数字，然后使用Object.keys获取密钥。filter只获取您想要的内容。由于Object.keys丢失了对象值，因此使用map从原始对象构建一个仅包含您想要的索引的数组。|offset|length|style|CODE|1080007|调试：|1080008|console.log(widthRange)
console.log(relevantKeys)
console.log(relevantValues)|1080009|entityMap^0|0|0|0|0|2|8|N|B|13|6|1L|B|27|3|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|10|8|@$M|11|N|12|O|P]|$M|13|N|14|O|P]|$M|15|N|16|O|P]|$M|17|N|18|O|P]|$M|19|N|1A|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1B|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1C|8|@]|9|@]|A|$E|F]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$]]

For your input data:

<pre><code>let widthRange = new Array()
widthRange[46] = { min:0, max:52 }
widthRange[61] = { min:52, max:70 }
widthRange[62] = { min:52, max:70 }
widthRange[63] = { min:52, max:70 }
widthRange[66] = { min:52, max:70 }
widthRange[90] = { min:70, max:94 }
</code></pre>

Declarative approach:

<pre><code>const relevantKeys = [46,66,90]
const relevantValues = Object.keys(widthRange)
 .filter(index =&gt; relevantKeys.includes(parseInt(index)))
 .map(relevantIndex =&gt; widthRange[relevantIndex])
</code></pre>

<code>Object.keys</code> to get the keys, using <code>parseInt</code> to cast them as numbers.
<code>filter</code> to get only ones you want.
<code>map</code> to build an array from the original object of just the indices you're after, since <code>Object.keys</code> loses the object values.

Debug:

<pre><code>console.log(widthRange)
console.log(relevantKeys)
console.log(relevantValues)
</code></pre>

blocks|key|1080036|text|这个问题由来已久，但现在你可以使用forEach，它很高效，可以将密钥保留为数字：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1080037|let+keys+=+widthRange.map((v,k)+=>+k).filter(i=>i!==undefined))|code-block|syntax|javascript|1080038|这将遍历widthRange并使用键的值生成一个新数组，然后通过只获取定义的值来过滤掉所有的稀疏槽。|1080039|(这不是个好主意，但对于棘手的问题:如果插槽0总是空的，可以缩短为filter(i=>i)或filter(Boolean)|offset|length|style|CODE|1080040|而且，它的效率可能较低，但可以使用let+keys+=+Object.keys(array).map(i=>i*1)进行数字转换|1080041|entityMap^0|0|0|0|X|C|1A|F|0|H|15|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@$K|W|L|X|M|N]|$K|Y|L|Z|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@$K|11|L|12|M|N]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|R|$]]

The question is pretty old, but nowadays you can use forEach, which is efficient and will retain the keys as numbers:
<pre><code>let keys = widthRange.map((v,k) =&gt; k).filter(i=&gt;i!==undefined))
</code></pre>
This loops through widthRange and makes a new array with the value of the keys, and then filters out all sparce slots by only taking the values that are defined.
(Bad idea, but for thorughness: If slot 0 was always empty, that could be shortened to <code>filter(i=&gt;i)</code> or <code>filter(Boolean)</code>
And, it may be less efficient, but the numbers can be cast with <code>let keys = Object.keys(array).map(i=&gt;i*1)</code>

blocks|key|1295109|text|要从数组的键生成数组，请使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1295110|Array.from(Array(10).keys());|code-block|syntax|javascript|1295111|上面的例子会给出一个从0到9的数组。这并不完全是你想要的，但我希望这能让你深入了解这个方法。|1295112|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|$]]

To generate an Array from an Array's keys, use
<pre class="lang-js prettyprint-override"><code>Array.from(Array(10).keys());
</code></pre>
The example above will give an array of 0 to 9. It is not exactly what you asked for but I hope this gives an insight into this method.

I have an array created with this code:

<pre><code>var widthRange = new Array();
widthRange[46] = { min:0, max:52 };
widthRange[66] = { min:52, max:70 };
widthRange[90] = { min:70, max:94 };
</code></pre>

I want to get each of the values 46, 66, 90 in a loop. I tried <code>for (var key in widthRange)</code> but this gives me a whole bunch of extra properties (I assume they are functions on the object). I can't use a regular for loop since the values are not sequential.

How to iterate array keys in Javascript?

Windows

我用下面的代码创建了一个数组：var widthRange = new Array();widthRange[46] = { min:0,  max:52 };widthRange[66] = { min:52, max:70 };widthRange[90] = { min:70, max:94 };我想在一个循环中...

问如何在Javascript中迭代数组键？
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