blocks|key|255333|text|您可以将switch语句与fall+thru一起使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|255334|switch+(test.type)+{

++case+"itema":
++case+"itemb":
++case+"itemc":
++case+"itemd":
++++//+do+something
}|code-block|syntax|javascript|255335|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 switch statement with fall thru:

<pre><code>switch (test.type) {

 case "itema":
 case "itemb":
 case "itemc":
 case "itemd":
 // do something
}
</code></pre>

blocks|key|255417|text|如果您正在与字符串进行比较，并且存在模式，请考虑使用正则表达式。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|255418|否则，我怀疑试图缩短它只会混淆你的代码。考虑简单地对行进行换行以使其更美观。|255419|if+(test.type+==+'itema'+%7C%7C
++++test.type+==+'itemb'+%7C%7C
++++test.type+==+'itemc'+%7C%7C
++++test.type+==+'itemd')+{
++++do+something.
}|code-block|syntax|javascript|255420|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|$]]

If you are comparing to strings and there is a pattern, consider using regular expressions.

Otherwise, I suspect attempting to shorten it will just obfuscate your code. Consider simply wrapping the lines to make it pretty.

<pre><code>if (test.type == 'itema' ||
 test.type == 'itemb' ||
 test.type == 'itemc' ||
 test.type == 'itemd') {
 do something.
}
</code></pre>

blocks|key|38691|text|var+possibilities+=+{
++"itema":+1,
++"itemb":+1,
++"itemc":+1,
…};
if+(test.type+in+possibilities)+{+…+}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|38692|将对象用作关联数组是一件很常见的事情，但由于JavaScript没有原生集合，因此也可以将对象用作廉价的集合。|unstyled|38693|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>var possibilities = {
 "itema": 1,
 "itemb": 1,
 "itemc": 1,
…};
if (test.type in possibilities) { … }
</code></pre>

Using an object as an associative array is a pretty common thing, but since JavaScript doesn't have a native set you can use objects as cheap sets as well.

blocks|key|38751|text|if(+/%5Eitem[a-d]$/.test(test.type)+)+{+/*+do+something+*/+}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|38752|或者，如果物品不是那么统一，那么：|unstyled|38753|if(+/%5E(itema%7Citemb%7Citemc%7Citemd)$/.test(test.type)+)+{+/*+do+something+*/+}|38754|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>if( /^item[a-d]$/.test(test.type) ) { /* do something */ }
</code></pre>

or if the items are not that uniform, then:

<pre><code>if( /^(itema|itemb|itemc|itemd)$/.test(test.type) ) { /* do something */ }
</code></pre>

blocks|key|38906|text|非常好的答案，但是您可以通过将其中一个包装在一个函数中来使代码更具可读性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|38907|这是一个复杂的if语句，当您(或其他人)在几年内阅读代码时，您将浏览以找到该部分以了解发生了什么。具有此业务逻辑级别的语句将导致您在确定正在测试的内容时出错几秒钟。像这样的代码，可以让你继续扫描。|38908|if(CheckIfBusinessRuleIsTrue())
{
++++//Do+Something
}

function+CheckIfBusinessRuleIsTrue()+
{
++++return+(the+best+solution+from+previous+posts+here);
}|code-block|syntax|javascript|38909|明确地命名你的函数，这样你正在测试的东西就会一目了然，你的代码也会更容易被扫描和理解。|38910|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Excellent answers, but you could make the code far more readable by wrapping one of them in a function.

This is complex if statement, when you (or someone else) read the code in a years time, you will be scanning through to find the section to understand what is happening. A statement with this level of business logic will cause you to stumble for a few seconds at while you work out what you are testing. Where as code like this, will allow you to continue scanning.

<pre><code>if(CheckIfBusinessRuleIsTrue())
{
 //Do Something
}

function CheckIfBusinessRuleIsTrue() 
{
 return (the best solution from previous posts here);
}
</code></pre>

Name your function explicitly so it immediately obvious what you are testing and your code will be much easier to scan and understand.

blocks|key|38860|text|您可以将所有答案放入Javascript+Set中，然后在集合上调用.contains()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|38861|你仍然需要声明所有的内容，但是内联调用会更短。|38862|类似于：|38863|var+itemSet+=+new+Set(["itema","itemb","itemc","itemd"]);
if(+itemSet.contains(+test.type+){}|code-block|syntax|javascript|38864|entityMap|0|LINK|mutability|MUTABLE|url|http://jsclass.jcoglan.com/set.html^0|Y|B|A|E|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|6|7|12|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|13|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|14|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

You could put all the answers into a <a href="http://jsclass.jcoglan.com/set.html" rel="nofollow">Javascript Set</a> and then just call <code>.contains()</code> on the set.

You still have to declare all the contents, but the inline call will be shorter. 

Something like:

<pre><code>var itemSet = new Set(["itema","itemb","itemc","itemd"]);
if( itemSet.contains( test.type ){}
</code></pre>

blocks|key|255384|text|我最喜欢的实现方法之一是使用underscore.js这样的库……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|255385|var+isItem+=+_.some(['itema','itemb','itemc','itemd'],+function(item)+{
++++return+test.type+===+item;
});

if(isItem)+{
++++//+One+of+them+was+true
}|code-block|syntax|javascript|255386|http://underscorejs.org/#some|offset|length|255387|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|T|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@$I|U|J|V|1|W]]|A|$]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|H]]]]

One of my favorite ways of accomplishing this is with a library such as underscore.js...

<pre><code>var isItem = _.some(['itema','itemb','itemc','itemd'], function(item) {
 return test.type === item;
});

if(isItem) {
 // One of them was true
}
</code></pre>

<a href="http://underscorejs.org/#some" rel="nofollow">http://underscorejs.org/#some</a>

blocks|key|255516|text|我发现的另一种或另一种很棒的方式是...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|255517|if+('a'+in+oc(['a','b','c']))+{+//dosomething+}

function+oc(a)
{
++var+o+=+{};
++for(var+i=0;i<a.length;i%2B%2B)++o[a[i]]='';
++return+o;
}|code-block|syntax|javascript|255518|当然，正如您所看到的，这使事情更进一步，并使它们更容易遵循逻辑。|255519|http://snook.ca/archives/javascript/testing_for_a_v|offset|length|255520|使用像~+&&+%7C%7C+(()，())+~~这样的运算符是很好的，只有当您的代码稍后中断时才可以。你不会知道从哪里开始。所以可读性很强。|255521|如果你必须这样做，你可以让它变得更短。|255522|('a'+in+oc(['a','b','c']))+&&+statement;
('a'+in+oc(['a','b','c']))+&&+(statements,statements);
('a'+in+oc(['a','b','c']))?statement:elseStatement;
('a'+in+oc(['a','b','c']))?(statements,statements):(elseStatements,elseStatements);|255523|如果你想反转|255524|('a'+in+oc(['a','b','c']))+%7C%7C+statement;|255525|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|0|1F|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|15|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|16|8|@]|9|@$K|17|L|18|1|19]]|A|$]]|$1|M|3|N|5|6|7|1A|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1B|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|1C|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|1D|8|@]|9|@]|A|$]]|$1|U|3|V|5|D|7|1E|8|@]|9|@]|A|$E|F]]|$1|W|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]]|X|$Y|$5|Z|10|11|A|$12|J]]]]

another way or another awesome way i found is this...

<pre><code>if ('a' in oc(['a','b','c'])) { //dosomething }

function oc(a)
{
 var o = {};
 for(var i=0;i&lt;a.length;i++) o[a[i]]='';
 return o;
}
</code></pre>

of course as you can see this takes things one step further and make them easy follow logic.

<a href="http://snook.ca/archives/javascript/testing_for_a_v" rel="nofollow">http://snook.ca/archives/javascript/testing_for_a_v</a>

using operators such as ~ &amp;&amp; || ((),()) ~~ is fine only if your code breaks later on. You won't know where to start. So readability is BIG.

if you must you could make it shorter. 

<pre><code>('a' in oc(['a','b','c'])) &amp;&amp; statement;
('a' in oc(['a','b','c'])) &amp;&amp; (statements,statements);
('a' in oc(['a','b','c']))?statement:elseStatement;
('a' in oc(['a','b','c']))?(statements,statements):(elseStatements,elseStatements);
</code></pre>

and if you want to do inverse

<pre><code>('a' in oc(['a','b','c'])) || statement;
</code></pre>

blocks|key|38941|text|只需使用switch语句而不是if语句：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|38942|switch+(test.type)+{

++case+"itema":case+"itemb":case+"itemc":case+"itemd":
++++//+do+your+process
++case+"other+cases":...:
++++//+do+other+processes
++default:
++++//+do+processes+when+test.type+does+not+meet+your+predictions.
}|code-block|syntax|javascript|38943|与在if中比较许多条件相比，Switch的运行速度也更快|38944|entityMap^0|4|6|F|2|0|0|2|2|E|6|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

Just use a <code>switch</code> statement instead of <code>if</code> statement:

<pre><code>switch (test.type) {

 case "itema":case "itemb":case "itemc":case "itemd":
 // do your process
 case "other cases":...:
 // do other processes
 default:
 // do processes when test.type does not meet your predictions.
}
</code></pre>

<code>Switch</code> also works faster than comparing lots of conditionals within an <code>if</code>

blocks|key|255786|text|对于非常长的字符串列表，这个想法将节省几个字符(并不是说我会在现实生活中推荐它，但它应该可以工作)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|255787|选择一个您知道不会出现在test.type中的字符，将其用作分隔符，将它们放入一个长字符串中，然后搜索该字符：|255788|if+("/itema/itemb/itemc/itemd/".indexOf("/"%2Btest.type%2B"/")>=0)+{
++//+doSomething
}|code-block|syntax|javascript|255789|如果字符串碰巧受到进一步的约束，您甚至可以省略分隔符...|255790|if+("itemaitembitemcitemd".indexOf(test.type)>=0)+{
++//+doSomething
}|255791|在这种情况下，你必须小心误报(例如，“...but”在那个版本中会匹配)|255792|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|$]]

For very long lists of strings, this idea would save a few characters (not saying I'd recommend it in real life, but it should work).

Choose a character that you know won't occur in your test.type, use it as a delimiter, stick them all into one long string and search that:

<pre><code>if ("/itema/itemb/itemc/itemd/".indexOf("/"+test.type+"/")&gt;=0) {
 // doSomething
}
</code></pre>

If your strings happen to be further constrained, you could even omit the delimiters...

<pre><code>if ("itemaitembitemcitemd".indexOf(test.type)&gt;=0) {
 // doSomething
}
</code></pre>

...but you'd have to be careful of false positives in that case (e.g. "embite" would match in that version)

blocks|key|39114|text|为了可读性，为测试创建一个函数(是的，一行函数)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|39115|function+isTypeDefined(test)+{
++++return+test.type+==+'itema'+%7C%7C
+++++++++++test.type+==+'itemb'+%7C%7C
+++++++++++test.type+==+'itemc'+%7C%7C
+++++++++++test.type+==+'itemd';
}|code-block|syntax|javascript|39116|那就叫它：|39117|…
++++if+(isTypeDefined(test))+{
…
}
...|39118|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|$]]

For readability create a function for the test (yes, a one line function):

<pre><code>function isTypeDefined(test) {
 return test.type == 'itema' ||
 test.type == 'itemb' ||
 test.type == 'itemc' ||
 test.type == 'itemd';
}
</code></pre>

then call it:

<pre><code>…
 if (isTypeDefined(test)) {
…
}
...
</code></pre>

blocks|key|39063|text|这可以通过一个简单的for循环来解决：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|39064|test+=+{};
test.type+=+'itema';

for(var+i=['itema','itemb','itemc'];+i[0]==test.type+&&+[
++++(function()+{
++++++++//+do+something
++++++++console.log('matched!');
++++})()
];+i.shift());|code-block|syntax|javascript|39065|我们使用for循环的第一部分来初始化您希望匹配的参数，使用第二部分来停止for循环的运行，使用第三部分来使循环最终退出。|39066|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|$]]

This can be solved with a simple for loop:

<pre class="lang-js prettyprint-override"><code>test = {};
test.type = 'itema';

for(var i=['itema','itemb','itemc']; i[0]==test.type &amp;&amp; [
 (function() {
 // do something
 console.log('matched!');
 })()
]; i.shift());
</code></pre>

We use the first section of the for loop to initialize the arguments you wish to match, the second section to stop the for loop from running, and the third section to cause the loop to eventually exit.

I have a very long conditional statement like the following:

<pre><code>if(test.type == 'itema' || test.type == 'itemb' || test.type == 'itemc' || test.type == 'itemd'){
 // do something.
}
</code></pre>

I was wondering if I could refactor this expression/statement into a more concise form.

Any idea on how to achieve this?

How to shorten my conditional statements

我有一个非常长的条件语句，如下所示：if(test.type == 'itema' || test.type == 'itemb' || test.type == 'itemc' || test.type == 'itemd'){    // do something.}我想知道我是否可以将这个表达式/语句重构为更简洁的形式。有关于如何实现这一点的想法吗？

问如何缩短我的条件语句
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回答 12

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