blocks|key|172539|text|它被称为条件运算符(因为它有三个操作数)和条件运算符(因为它是一个if/++/)运算符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|172540|它的计算结果是一个值，因此通常使用它来赋值，例如：|172541|var+result+=+condition+?+value1+:+value2;|code-block|syntax|javascript|172542|相当于：|172543|var+result;
if+(condition+==+true)+{
++result+=+value1;
}+else+{
++result+=+value2;
}|172544|举个例子：|172545|var+message+=+"Length+is+"+%2B+len+%2B+"+"+%2B+(len==1+?+"foot"+:+"feet");|172546|注意：?:是全运算符。它不是?和:运算符，所以?本身在Javascript中是没有意义的。|CODE|172547|entityMap^0|13|5|0|0|P|0|0|0|4|0|0|0|5|0|0|0|19|3|2|E|1|G|1|N|1|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|15|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|19|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|1D|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|W]|$9|1J|A|1K|B|W]|$9|1L|A|1M|B|W]|$9|1N|A|1O|B|W]]|D|@]|E|$]]|$1|X|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]]|Y|$]]

It's known as a <a href="http://en.wikipedia.org/wiki/Ternary_operation" rel="nofollow noreferrer">ternary</a> (because it has three operands) conditional (because it's an if/else/then) operator.

It is evaluated to a value, so you would usually use it to assign a value, such as:

<pre><code>var result = condition ? value1 : value2;
</code></pre>

Which is equivalent to:

<pre><code>var result;
if (condition == true) {
 result = value1;
} else {
 result = value2;
}
</code></pre>

An example:

<pre><code>var message = "Length is " + len + " " + (len==1 ? "foot" : "feet");
</code></pre>

Note <code>?:</code> is the full operator. It's not a <code>?</code> and <code>:</code> operator, so <code>?</code> by itself is meaningless in Javascript.

blocks|key|172390|text|它是一个条件运算符。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|172391|它是|172392|如果为var1，则为var2否则为var3|172393|点击此处阅读更多信息|172394|Conditional+Operator|offset|length|172395|172396|条件运算符是唯一接受三个操作数的JavaScript运算符。此运算符经常用作if语句的快捷方式。|blockquote|172397|172398|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Operators/Special_Operators/Conditional_Operator^0|0|0|0|0|0|K|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|11|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|12|8|@]|9|@$J|13|K|14|1|15]]|A|$]]|$1|L|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|17|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|18|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

Its a conditional operator.

It is 

if var1 then var2 else var3

Read more here

<a href="https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Operators/Special_Operators/Conditional_Operator" rel="nofollow noreferrer">Conditional Operator</a>

<blockquote>
 The conditional operator is the only
 JavaScript operator that takes three
 operands. This operator is frequently
 used as a shortcut for the if
 statement.
</blockquote>

blocks|key|1651999|text|if(var1)+{
++++var2;
else+{
++++var3;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1652000|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

blocks|key|1578618|text|如果var1+?+var2+:+var3被认为具有等同于var2的值，则表达式var1返回true的值，否则返回var3的值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1578619|请注意，这与以下内容不完全相同：|1578620|if+(var1)
+++varX+=+var2
else
+++varX+=+var3|code-block|syntax|javascript|1578621|因为上面的构造本身不能作为更大表达式的一部分出现。|1578622|在ternery表达式中，也就是众所周知的?+:，应该避免允许组件表达式产生%2B%2B或--操作符以外的副作用。例如，这不是一个好主意：|1578623|varX+=+var1+?+doSomethingSignificant()+:+doSomethingElseSignificant();|1578624|在这种情况下，最好使用if+else构造。在手上：-|1578625|varX+=+var1+?+calcSomething(var2)+:+someOtherCalc(var2);|1578626|假设被调用的函数本身不会显着修改程序状态，这是可以接受的。|1578627|编辑|BOLD|1578628|我认为我需要再次强调这一点。Do+not使用三元运算符作为缩短if语句的方法。这两者有不同的目的。如果您的代码充满了本应为if+else的?+:，将很难阅读。我们希望逻辑流出现在if语句中。当表达式有一个简单的逻辑部分时，我们期望使用?+:。注意:表达式不会修改事物，只有它们的结果在赋值时才会修改事物。|1578629|entityMap^0|2|I|S|4|13|4|19|4|1K|4|0|0|0|0|L|3|0|0|B|7|0|0|0|0|2|0|H|3|V|2|1P|7|1X|3|2H|2|39|3|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1G|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1H|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1I|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1J|8|@$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|J|7|1M|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|1N|8|@$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|U|3|V|5|J|7|1Q|8|@]|D|@]|E|$K|L]]|$1|W|3|X|5|6|7|1R|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|6|7|1S|8|@$9|1T|A|1U|B|10]]|D|@]|E|$]]|$1|11|3|12|5|6|7|1V|8|@$9|1W|A|1X|B|10]|$9|1Y|A|1Z|B|C]|$9|20|A|21|B|C]|$9|22|A|23|B|C]|$9|24|A|25|B|C]|$9|26|A|27|B|C]]|D|@]|E|$]]|$1|13|3|-4|5|6|7|28|8|@]|D|@]|E|$]]]|14|$]]

The expression <code>var1 ? var2 : var3</code> returns the value of <code>var2</code> if <code>var1</code> is considered to have a value equivalent to <code>true</code> else it returns teh value of <code>var3</code>.

Note this is not quite the same as:-

<pre><code>if (var1)
 varX = var2
else
 varX = var3
</code></pre>

Since the above construct can not itself appear as part of a larger expression.

In ternery expression, as <code>? :</code> is known, one should avoid allowing the component expressions to have side effects other than perhaps the side-effects of ++ or -- operators. For example this isn't a good idea:-

<pre><code>varX = var1 ? doSomethingSignificant() : doSomethingElseSignificant();
</code></pre>

In this case it would be better to use the <code>if else</code> construct. On the hand:-

<pre><code>varX = var1 ? calcSomething(var2) : someOtherCalc(var2);
</code></pre>

this is acceptable assuming the called functions don't themselves modify the program state significantly.

Edit:

I think I need to re-enforce this point. Do not use the ternary operator as means to short cut on <code>if</code> statements. The two have different purposes. If your code is full of <code>? :</code> that should be <code>if else</code> it will be difficult to read. We expect logical flow to appear in <code>if</code> statements. We expect <code>? :</code> when there is a simple logical component to an expression. Note expressions do not modify things only the results of them when assigned should modify things.

blocks|key|352605|text|作为第一个问题的补充，您也可以使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|352606|++var+result+=+(condition)+&&+var1+%7C%7C+var2;|code-block|syntax|javascript|352607|并获得相同的结果|352608|对于第二个问题，在C中也可以使用下面的代码：|352609|++(condition)+&&+someinstruction;|352610|但这似乎不适用于javascript+(至少在我的firefox版本上)。|352611|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

As an addendum for the first question, you can alternatively use 

<pre><code> var result = (condition) &amp;&amp; var1 || var2;
</code></pre>

and obtain the same result

For the second question, in C the following works too :

<pre><code> (condition) &amp;&amp; someinstruction;
</code></pre>

but that does not seem to work in javascript (at least with my version of firefox).

blocks|key|1578566|text|这似乎是一种三元运算。可以这么说，if+else操作的简短形式。有关详细信息，请查看here+...|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1578567|entityMap|0|LINK|mutability|MUTABLE|url|http://www.hscripts.com/tutorials/javascript/ternary.php^0|16|4|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

This seems to be sort of a ternary operation. Short form of an if else operation, so to say. check <a href="http://www.hscripts.com/tutorials/javascript/ternary.php" rel="nofollow noreferrer">here</a> for details...

I've seen this format used in <a href="http://en.wikipedia.org/wiki/JavaScript" rel="nofollow noreferrer">JavaScript</a> code, but can't find a good source for the meaning.

Edit for a follow-up:

Thanks for all the quick answers! I figured it was something like that. Now, for bonus points:

can you use 
 (var1 ? var2)

to do the same thing as

<pre><code> if (var1) {
 var2
 }
</code></pre>

?

How do you read this JavaScript code? (var1 ? var2:var3)

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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我在代码中见过这种格式，但是找不到一个很好的来源来表达它的含义。编辑以进行后续操作：感谢您的快速回答！我想应该是这样的。现在，让我们来看看加分：你能使用(var1？var2)做同样的事情    if (var1) {        var2    }

问如何阅读这段JavaScript代码？(var1？var2:var3)
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