blocks|key|761696|text|您可以使用JSON.parse或jQuery.parseJSON，并使用如下代码查看它是否返回true：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|761697|function+test+(input)+{
++++try+{
++++++++return+!!$.parseJSON(input.toLowerCase());
++++}+catch+(e)+{+}
}|code-block|syntax|javascript|761698|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|$]]

You can use JSON.parse or jQuery.parseJSON and see if it returns true using something like this:

<pre><code>function test (input) {
 try {
 return !!$.parseJSON(input.toLowerCase());
 } catch (e) { }
}
</code></pre>

blocks|key|977273|text|这取决于您希望函数如何工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|977274|如果您只想测试字符串中的单词'true‘，并将没有该单词的任何字符串(或非字符串)定义为false，最简单的方法可能是：|977275|function+parseBoolean(str)+{
++return+/true/i.test(str);
}|code-block|syntax|javascript|977276|如果您希望确保整个字符串都是单词true，您可以这样做：|977277|function+parseBoolean(str)+{
++return+/%5Etrue$/i.test(str);
}|977278|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

It depends how you wish the function to work.

If all you wish to do is test for the word 'true' inside the string, and define any string (or nonstring) that doesn't have it as false, the easiest way is probably this:

<pre><code>function parseBoolean(str) {
 return /true/i.test(str);
}
</code></pre>

If you wish to assure that the entire string is the word true you could do this:

<pre><code>function parseBoolean(str) {
 return /^true$/i.test(str);
}
</code></pre>

blocks|key|761742|text|就我个人而言，我认为这并不好，你的函数将无效值“隐藏”为false，并且--取决于你的用例--不会为"1"返回true。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|761743|另一个问题可能是它会吐在任何不是字符串的东西上。|761744|我会使用类似这样的东西：|761745|function+parseBool(value)+{
++if+(typeof+value+===+"string")+{
+++++value+=+value.replace(/%5E\s%2B%7C\s%2B$/g,+"").toLowerCase();
+++++if+(value+===+"true"+%7C%7C+value+===+"false")
+++++++return+value+===+"true";
++}
++return;+//+returns+undefined
}|code-block|syntax|javascript|761746|并根据用例对其进行扩展，以区分"0"和"1"。|761747|(也许有一种方法可以只与"true"比较一次，但我现在想不出什么。)|761748|entityMap^0|S|5|1E|3|1J|4|0|0|0|0|F|3|J|3|0|C|6|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|12|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|13|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|T|$]]

Personally I think it's not good, that your function "hides" invalid values as <code>false</code> and - depending on your use cases - doesn't return <code>true</code> for <code>"1"</code>.

Another problem could be that it barfs on anything that's not a string.

I would use something like this:

<pre><code>function parseBool(value) {
 if (typeof value === "string") {
 value = value.replace(/^\s+|\s+$/g, "").toLowerCase();
 if (value === "true" || value === "false")
 return value === "true";
 }
 return; // returns undefined
}
</code></pre>

And depending on the use cases extend it to distinguish between <code>"0"</code> and <code>"1"</code>.

(Maybe there is a way to compare only once against <code>"true"</code>, but I couldn't think of something right now.)

blocks|key|761758|text|您可以尝试以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|761759|function+parseBool(val)
{
++++if+((typeof+val+===+'string'+&&+(val.toLowerCase()+===+'true'+%7C%7C+val.toLowerCase()+===+'yes'))+%7C%7C+val+===+1)
++++++++return+true;
++++else+if+((typeof+val+===+'string'+&&+(val.toLowerCase()+===+'false'+%7C%7C+val.toLowerCase()+===+'no'))+%7C%7C+val+===+0)
++++++++return+false;

++++return+null;
}|code-block|syntax|javascript|761760|如果它是一个有效值，则返回等价的布尔值，否则返回null。|761761|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|$]]

You can try the following:

<pre><code>function parseBool(val)
{
 if ((typeof val === 'string' &amp;&amp; (val.toLowerCase() === 'true' || val.toLowerCase() === 'yes')) || val === 1)
 return true;
 else if ((typeof val === 'string' &amp;&amp; (val.toLowerCase() === 'false' || val.toLowerCase() === 'no')) || val === 0)
 return false;

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

If it's a valid value, it returns the equivalent bool value otherwise it returns null.

blocks|key|761784|text|为什么不保持简单呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|761785|var+parseBool+=+function(str)+{
++++if+(typeof+str+===+'string'+&&+str.toLowerCase()+==+'true')
++++++++++++return+true;

++++return+(parseInt(str)+>+0);
}|code-block|syntax|javascript|761786|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|$]]

Why not keep it simple?

<pre><code>var parseBool = function(str) {
 if (typeof str === 'string' &amp;&amp; str.toLowerCase() == 'true')
 return true;

 return (parseInt(str) &gt; 0);
}
</code></pre>

blocks|key|977397|text|足以使用eval+javascript函数将字符串转换为布尔值|type|unstyled|depth|inlineStyleRanges|entityRanges|data|977398|eval('true')++
eval('false')|code-block|syntax|javascript|977399|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|$]]

Enough to using eval javascript function to convert string to boolean 

<pre><code>eval('true') 
eval('false')
</code></pre>

blocks|key|761914|text|木眼要当心。在看完所有这些代码后，我觉得有义务发布：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|761915|让我们从最短但非常严格的方式开始：|761916|var+str+=+"true";
var+mybool+=+JSON.parse(str);|code-block|syntax|javascript|761917|并以一种适当的、更宽容的方式结束：|761918|var+parseBool+=+function(str)+
{
++++//+console.log(typeof+str);
++++//+strict:+JSON.parse(str)

++++if(str+==+null)
++++++++return+false;

++++if+(typeof+str+===+'boolean')
++++{
++++++++if(str+===+true)
++++++++++++return+true;

++++++++return+false;
++++}+

++++if(typeof+str+===+'string')
++++{
++++++++if(str+==+"")
++++++++++++return+false;

++++++++str+=+str.replace(/%5E\s%2B%7C\s%2B$/g,+'');
++++++++if(str.toLowerCase()+==+'true'+%7C%7C+str.toLowerCase()+==+'yes')
++++++++++++return+true;

++++++++str+=+str.replace(/,/g,+'.');
++++++++str+=+str.replace(/%5E\s*\-\s*/g,+'-');
++++}

++++//+var+isNum+=+string.match(/%5E[0-9]%2B$/)+!=+null;
++++//+var+isNum+=+/%5E\d%2B$/.test(str);
++++if(!isNaN(str))
++++++++return+(parseFloat(str)+!=+0);

++++return+false;
}|761919|测试：|761920|var+array_1+=+new+Array(true,+1,+"1",-1,+"-1",+"+-+1",+"true",+"TrUe",+"++true++",+"++TrUe",+1/0,+"1.5",+"1,5",+1.5,+5,+-3,+-0.1,+0.1,+"+-+0.1",+Infinity,+"Infinity",+-Infinity,+"-Infinity","+-+Infinity",+"+yEs");

var+array_2+=+new+Array(null,+"",+false,+"false",+"+++false+++",+"+f+alse",+"FaLsE",+0,+"00",+"1/0",+0.0,+"0.0",+"0,0",+"100a",+"1+00",+"+0+",+0.0,+"0.0",+-0.0,+"-0.0",+"+-1a+",+"abc");


for(var+i+=0;+i+<+array_1.length;%2B%2Bi){+console.log("array_1["%2Bi%2B"]+("%2Barray_1[i]%2B"):+"+%2B+parseBool(array_1[i]));}

for(var+i+=0;+i+<+array_2.length;%2B%2Bi){+console.log("array_2["%2Bi%2B"]+("%2Barray_2[i]%2B"):+"+%2B+parseBool(array_2[i]));}

for(var+i+=0;+i+<+array_1.length;%2B%2Bi){+console.log(parseBool(array_1[i]));}
for(var+i+=0;+i+<+array_2.length;%2B%2Bi){+console.log(parseBool(array_2[i]));}|761921|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Wood-eye be careful. 
After looking at all this code, I feel obligated to post:

Let's start with the shortest, but very strict way:

<pre><code>var str = "true";
var mybool = JSON.parse(str);
</code></pre>

And end with a proper, more tolerant way:

<pre><code>var parseBool = function(str) 
{
 // console.log(typeof str);
 // strict: JSON.parse(str)

 if(str == null)
 return false;

 if (typeof str === 'boolean')
 {
 if(str === true)
 return true;

 return false;
 } 

 if(typeof str === 'string')
 {
 if(str == "")
 return false;

 str = str.replace(/^\s+|\s+$/g, '');
 if(str.toLowerCase() == 'true' || str.toLowerCase() == 'yes')
 return true;

 str = str.replace(/,/g, '.');
 str = str.replace(/^\s*\-\s*/g, '-');
 }

 // var isNum = string.match(/^[0-9]+$/) != null;
 // var isNum = /^\d+$/.test(str);
 if(!isNaN(str))
 return (parseFloat(str) != 0);

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

Testing:

<pre><code>var array_1 = new Array(true, 1, "1",-1, "-1", " - 1", "true", "TrUe", " true ", " TrUe", 1/0, "1.5", "1,5", 1.5, 5, -3, -0.1, 0.1, " - 0.1", Infinity, "Infinity", -Infinity, "-Infinity"," - Infinity", " yEs");

var array_2 = new Array(null, "", false, "false", " false ", " f alse", "FaLsE", 0, "00", "1/0", 0.0, "0.0", "0,0", "100a", "1 00", " 0 ", 0.0, "0.0", -0.0, "-0.0", " -1a ", "abc");


for(var i =0; i &lt; array_1.length;++i){ console.log("array_1["+i+"] ("+array_1[i]+"): " + parseBool(array_1[i]));}

for(var i =0; i &lt; array_2.length;++i){ console.log("array_2["+i+"] ("+array_2[i]+"): " + parseBool(array_2[i]));}

for(var i =0; i &lt; array_1.length;++i){ console.log(parseBool(array_1[i]));}
for(var i =0; i &lt; array_2.length;++i){ console.log(parseBool(array_2[i]));}
</code></pre>

blocks|key|762019|text|我喜欢RoToRa提供的解决方案(如果值有任何布尔含义，请尝试解析给定值，否则请不要解析)。尽管如此，我想提供一些小的修改，让它或多或少像C#中的Boolean.TryParse一样工作，它支持out参数。在JavaScript中，它可以通过以下方式实现：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|762020|var+BoolHelpers+=+{
++++tryParse:+function+(value)+{
++++++++if+(typeof+value+==+'boolean'+%7C%7C+value+instanceof+Boolean)
++++++++++++return+value;
++++++++if+(typeof+value+==+'string'+%7C%7C+value+instanceof+String)+{
++++++++++++value+=+value.trim().toLowerCase();
++++++++++++if+(value+===+'true'+%7C%7C+value+===+'false')
++++++++++++++++return+value+===+'true';
++++++++}
++++++++return+{+error:+true,+msg:+'Parsing+error.+Given+value+has+no+boolean+meaning.'+}
++++}
}|code-block|syntax|javascript|762021|用法：|762022|var+result+=+BoolHelpers.tryParse("false");
if+(result.error)+alert(result.msg);|762023|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.boolean.tryparse.aspx^0|2P|3|21|G|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

I like the solution provided by RoToRa (try to parse given value, if it has any boolean meaning, otherwise - don't). Nevertheless I'd like to provide small modification, to have it working more or less like <a href="http://msdn.microsoft.com/en-us/library/system.boolean.tryparse.aspx" rel="nofollow">Boolean.TryParse</a> in C#, which supports <code>out</code> params. In JavaScript it can be implemented in the following manner:

<pre><code>var BoolHelpers = {
 tryParse: function (value) {
 if (typeof value == 'boolean' || value instanceof Boolean)
 return value;
 if (typeof value == 'string' || value instanceof String) {
 value = value.trim().toLowerCase();
 if (value === 'true' || value === 'false')
 return value === 'true';
 }
 return { error: true, msg: 'Parsing error. Given value has no boolean meaning.' }
 }
}
</code></pre>

The usage:

<pre><code>var result = BoolHelpers.tryParse("false");
if (result.error) alert(result.msg);
</code></pre>

blocks|key|977681|text|stringjs有一个toBoolean()方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|977682|http://stringjs.com/#methods/toboolean-tobool|offset|length|977683|S('true').toBoolean()+//true
S('false').toBoolean()+//false
S('hello').toBoolean()+//false
S(true).toBoolean()+//true
S('on').toBoolean()+//true
S('yes').toBoolean()+//true
S('TRUE').toBoolean()+//true
S('TrUe').toBoolean()+//true
S('YES').toBoolean()+//true
S('ON').toBoolean()+//true
S('').toBoolean()+//false
S(undefined).toBoolean()+//false
S('undefined').toBoolean()+//false
S(null).toBoolean()+//false
S(false).toBoolean()+//false
S({}).toBoolean()+//false
S(1).toBoolean()+//true
S(-1).toBoolean()+//false
S(0).toBoolean()+//false|code-block|syntax|javascript|977684|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|19|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@$D|T|E|U|1|V]]|A|$]]|$1|F|3|G|5|H|7|W|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|C]]]]

stringjs has a toBoolean() method:

<a href="http://stringjs.com/#methods/toboolean-tobool" rel="nofollow">http://stringjs.com/#methods/toboolean-tobool</a>

<pre><code>S('true').toBoolean() //true
S('false').toBoolean() //false
S('hello').toBoolean() //false
S(true).toBoolean() //true
S('on').toBoolean() //true
S('yes').toBoolean() //true
S('TRUE').toBoolean() //true
S('TrUe').toBoolean() //true
S('YES').toBoolean() //true
S('ON').toBoolean() //true
S('').toBoolean() //false
S(undefined).toBoolean() //false
S('undefined').toBoolean() //false
S(null).toBoolean() //false
S(false).toBoolean() //false
S({}).toBoolean() //false
S(1).toBoolean() //true
S(-1).toBoolean() //false
S(0).toBoolean() //false
</code></pre>

blocks|key|762191|text|您可以添加以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|762192|function+parseBool(str)+{

++if+(str.length+==+null)+{
++++return+str+==+1+?+true+:+false;
++}+else+{
++++return+str+==+"true"+?+true+:+false;
++}

}|code-block|syntax|javascript|762193|其工作原理如下：|762194|parseBool(1)+//true
parseBool(0)+//false
parseBool("true")+//true
parseBool("false")+//false|762195|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|$]]

You can add this code:

<pre><code>function parseBool(str) {

 if (str.length == null) {
 return str == 1 ? true : false;
 } else {
 return str == "true" ? true : false;
 }

}
</code></pre>

Works like this:

<pre><code>parseBool(1) //true
parseBool(0) //false
parseBool("true") //true
parseBool("false") //false
</code></pre>

blocks|key|762221|text|您可以使用JSON.parse来实现此目的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|762222|JSON.parse("true");+//returns+boolean+true|code-block|syntax|javascript|762223|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|$]]

You can use JSON.parse for that:

<pre><code>JSON.parse("true"); //returns boolean true
</code></pre>

blocks|key|762277|text|我不知羞耻地将Apache+Common's+toBoolean转换为JavaScript：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|762278|JSFiddle：https://jsfiddle.net/m2efvxLm/1/|762279|代码：|762280|​|762281|function+toBoolean(str)+{
++if+(str+==+"true")+{
++++return+true;
++}
++if+(!str)+{
++++return+false;
++}
++switch+(str.length)+{
++++case+1:+{
++++++var+ch0+=+str.charAt(0);
++++++if+(ch0+==+'y'+%7C%7C+ch0+==+'Y'+%7C%7C
++++++++++ch0+==+'t'+%7C%7C+ch0+==+'T'+%7C%7C
++++++++++ch0+==+'1')+{
++++++++return+true;
++++++}
++++++if+(ch0+==+'n'+%7C%7C+ch0+==+'N'+%7C%7C
++++++++++ch0+==+'f'+%7C%7C+ch0+==+'F'+%7C%7C
++++++++++ch0+==+'0')+{
++++++++return+false;
++++++}
++++++break;
++++}
++++case+2:+{
++++++var+ch0+=+str.charAt(0);
++++++var+ch1+=+str.charAt(1);
++++++if+((ch0+==+'o'+%7C%7C+ch0+==+'O')+&&
++++++++++(ch1+==+'n'+%7C%7C+ch1+==+'N')+)+{
++++++++return+true;
++++++}
++++++if+((ch0+==+'n'+%7C%7C+ch0+==+'N')+&&
++++++++++(ch1+==+'o'+%7C%7C+ch1+==+'O')+)+{
++++++++return+false;
++++++}
++++++break;
++++}
++++case+3:+{
++++++var+ch0+=+str.charAt(0);
++++++var+ch1+=+str.charAt(1);
++++++var+ch2+=+str.charAt(2);
++++++if+((ch0+==+'y'+%7C%7C+ch0+==+'Y')+&&
++++++++++(ch1+==+'e'+%7C%7C+ch1+==+'E')+&&
++++++++++(ch2+==+'s'+%7C%7C+ch2+==+'S')+)+{
++++++++return+true;
++++++}
++++++if+((ch0+==+'o'+%7C%7C+ch0+==+'O')+&&
++++++++++(ch1+==+'f'+%7C%7C+ch1+==+'F')+&&
++++++++++(ch2+==+'f'+%7C%7C+ch2+==+'F')+)+{
++++++++return+false;
++++++}
++++++break;
++++}
++++case+4:+{
++++++var+ch0+=+str.charAt(0);
++++++var+ch1+=+str.charAt(1);
++++++var+ch2+=+str.charAt(2);
++++++var+ch3+=+str.charAt(3);
++++++if+((ch0+==+'t'+%7C%7C+ch0+==+'T')+&&
++++++++++(ch1+==+'r'+%7C%7C+ch1+==+'R')+&&
++++++++++(ch2+==+'u'+%7C%7C+ch2+==+'U')+&&
++++++++++(ch3+==+'e'+%7C%7C+ch3+==+'E')+)+{
++++++++return+true;
++++++}
++++++break;
++++}
++++case+5:+{
++++++var+ch0+=+str.charAt(0);
++++++var+ch1+=+str.charAt(1);
++++++var+ch2+=+str.charAt(2);
++++++var+ch3+=+str.charAt(3);
++++++var+ch4+=+str.charAt(4);
++++++if+((ch0+==+'f'+%7C%7C+ch0+==+'F')+&&
++++++++++(ch1+==+'a'+%7C%7C+ch1+==+'A')+&&
++++++++++(ch2+==+'l'+%7C%7C+ch2+==+'L')+&&
++++++++++(ch3+==+'s'+%7C%7C+ch3+==+'S')+&&
++++++++++(ch4+==+'e'+%7C%7C+ch4+==+'E')+)+{
++++++++return+false;
++++++}
++++++break;
++++}
++++default:
++++++break;
++}

++return+false;
}
console.log(toBoolean("yEs"));+//+true
console.log(toBoolean("yES"));+//+true
console.log(toBoolean("no"));+//+false
console.log(toBoolean("NO"));+//+false
console.log(toBoolean("on"));+//+true
console.log(toBoolean("oFf"));+//+false|code-block|syntax|javascript|762282|Inspect+this+element,+and+view+the+console+output.|762283|762284|entityMap|0|LINK|mutability|MUTABLE|url|https://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/BooleanUtils.html|1|https://jsfiddle.net/m2efvxLm/1/^0|N|9|7|P|0|0|9|W|1|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@$9|16|A|17|1|18]]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|H|3|I|5|6|7|1D|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|1E|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1F|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|N|7|1G|8|@]|D|@]|E|$O|P]]|$1|S|3|K|5|6|7|1H|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]|11|$5|W|X|Y|E|$Z|12]]]]

I shamelessly converted <a href="https://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/BooleanUtils.html" rel="nofollow">Apache Common's <code>toBoolean</code></a> to JavaScript:

JSFiddle: <a href="https://jsfiddle.net/m2efvxLm/1/" rel="nofollow">https://jsfiddle.net/m2efvxLm/1/</a>

Code:

<div class="snippet" data-lang="js" data-hide="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function toBoolean(str) {
 if (str == "true") {
 return true;
 }
 if (!str) {
 return false;
 }
 switch (str.length) {
 case 1: {
 var ch0 = str.charAt(0);
 if (ch0 == 'y' || ch0 == 'Y' ||
 ch0 == 't' || ch0 == 'T' ||
 ch0 == '1') {
 return true;
 }
 if (ch0 == 'n' || ch0 == 'N' ||
 ch0 == 'f' || ch0 == 'F' ||
 ch0 == '0') {
 return false;
 }
 break;
 }
 case 2: {
 var ch0 = str.charAt(0);
 var ch1 = str.charAt(1);
 if ((ch0 == 'o' || ch0 == 'O') &amp;&amp;
 (ch1 == 'n' || ch1 == 'N') ) {
 return true;
 }
 if ((ch0 == 'n' || ch0 == 'N') &amp;&amp;
 (ch1 == 'o' || ch1 == 'O') ) {
 return false;
 }
 break;
 }
 case 3: {
 var ch0 = str.charAt(0);
 var ch1 = str.charAt(1);
 var ch2 = str.charAt(2);
 if ((ch0 == 'y' || ch0 == 'Y') &amp;&amp;
 (ch1 == 'e' || ch1 == 'E') &amp;&amp;
 (ch2 == 's' || ch2 == 'S') ) {
 return true;
 }
 if ((ch0 == 'o' || ch0 == 'O') &amp;&amp;
 (ch1 == 'f' || ch1 == 'F') &amp;&amp;
 (ch2 == 'f' || ch2 == 'F') ) {
 return false;
 }
 break;
 }
 case 4: {
 var ch0 = str.charAt(0);
 var ch1 = str.charAt(1);
 var ch2 = str.charAt(2);
 var ch3 = str.charAt(3);
 if ((ch0 == 't' || ch0 == 'T') &amp;&amp;
 (ch1 == 'r' || ch1 == 'R') &amp;&amp;
 (ch2 == 'u' || ch2 == 'U') &amp;&amp;
 (ch3 == 'e' || ch3 == 'E') ) {
 return true;
 }
 break;
 }
 case 5: {
 var ch0 = str.charAt(0);
 var ch1 = str.charAt(1);
 var ch2 = str.charAt(2);
 var ch3 = str.charAt(3);
 var ch4 = str.charAt(4);
 if ((ch0 == 'f' || ch0 == 'F') &amp;&amp;
 (ch1 == 'a' || ch1 == 'A') &amp;&amp;
 (ch2 == 'l' || ch2 == 'L') &amp;&amp;
 (ch3 == 's' || ch3 == 'S') &amp;&amp;
 (ch4 == 'e' || ch4 == 'E') ) {
 return false;
 }
 break;
 }
 default:
 break;
 }

 return false;
}
console.log(toBoolean("yEs")); // true
console.log(toBoolean("yES")); // true
console.log(toBoolean("no")); // false
console.log(toBoolean("NO")); // false
console.log(toBoolean("on")); // true
console.log(toBoolean("oFf")); // false</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>Inspect this element, and view the console output.</code></pre>
</div>
</div>

blocks|key|762357|text|最后但并非最不重要的一点是，使用默认值执行此操作的简单而有效的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|762358|ES5|762359|function+parseBool(value,+defaultValue)+{
++++return+(value+==+'true'+%7C%7C+value+==+'false'+%7C%7C+value+===+true+%7C%7C+value+===+false)+&&+JSON.parse(value)+%7C%7C+defaultValue;
}|code-block|syntax|javascript|762360|ES6，一种较短的班轮|762361|const+parseBool+=+(value,+defaultValue)+=>+['true',+'false',+true,+false].includes(value)+&&+JSON.parse(value)+%7C%7C+defaultValue|762362|JSON.parse是解析布尔值的有效方法|762363|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

last but not least, a simple and efficient way to do it with a default value :

ES5

<pre><code>function parseBool(value, defaultValue) {
 return (value == 'true' || value == 'false' || value === true || value === false) &amp;&amp; JSON.parse(value) || defaultValue;
}
</code></pre>

ES6 , a shorter one liner

<pre><code>const parseBool = (value, defaultValue) =&gt; ['true', 'false', true, false].includes(value) &amp;&amp; JSON.parse(value) || defaultValue
</code></pre>

JSON.parse is efficient to parse booleans

JavaScript has <code>parseInt()</code> and <code>parseFloat()</code>, but there's no <code>parseBool</code> or <code>parseBoolean</code> method in the global scope, as far as I'm aware.

I need a method that takes strings with values like "true" or "false" and returns a JavaScript <code>Boolean</code>.

Here's my implementation:

<pre><code>function parseBool(value) {
 return (typeof value === "undefined") ? 
 false : 
 // trim using jQuery.trim()'s source 
 value.replace(/^\s+|\s+$/g, "").toLowerCase() === "true";
}
</code></pre>

Is this a good function? Please give me your feedback.

Thanks!

JavaScript: Parsing a string Boolean value?

jQuery

JSON

JavaScript有parseInt()和parseFloat()，但据我所知，全局作用域中没有parseBool或parseBoolean方法。我需要一个方法，它接受像"true“或"false”这样的值的字符串，并返回一个JavaScript Boolean。下面是我的实现：function parseBool(...

问JavaScript:解析字符串布尔值？
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