带有多个逗号分隔值的return语句 [英] return statement with multiple comma separated values
问题描述
可能重复:
Javascript语法:逗号是什么意思?
这是什么模式回归?它是如何工作的?
What does this pattern return? How does it work?
返回myfunc(),myobj.myvar = someobj.prop,myobj
之前我没有遇到过这种模式,但一直在查看Bing Maps Ajax Control,并且多次注意到这种模式。
I have not come across this pattern before but have been looking at the Bing Maps Ajax Control and have noticed this pattern several times.
据我所知,不会返回多个值。那么这种模式有什么作用呢?什么回来了?这种模式的好处是什么?
As I understand it multiple values are not returned. So what does this pattern do? What is returned? What is this pattern's benefit?
推荐答案
这是逗号运算符。它评估其左侧操作数,抛出结果,评估其右侧操作数,并将其作为结果值。它是从左到右的关联,所以 a,b,c
评估 a
,然后 b
,然后 c
,并将 c
的结果作为其值。
It's the comma operator. It evaluates its left-hand operand, throws the result away, evalutes its right-hand operand, and takes that as its result value. It's left-to-right associative, so a, b, c
evaluates a
, then b
, then c
, and takes the result of c
as its value.
在你的例子中,它完全像:
In your example, it's exactly like:
myfunc();
myobj.myvar = someobj.prop;
return myobj;
有些人真的更喜欢在一条线上做事,即使没有客观理由。你给出的例子没有任何好处,实际上它让人感到困惑,因为它看起来像前两位与最终返回的值有关,而它们却没有。 (我写的)在你告诉我们之前它是缩小的代码;显然,对人类不清楚只是源代码中的一个问题,而不是缩小代码。)
既然你我说它是一个缩小器:如果这是条件块的一部分,缩小器可能获得的非常小可能的好处:它可以保存一个或两个字符。如果我们假设长格式如下所示:
Since you've said it's a minifier: The very small possible benefit the minifier might have gotten there is if this is part of a conditional block: It can save one or two characters. If we assume the long form looked like this:
if (someCondition) {
myfunc();
myobj.myvar = someobj.prop;
return myobj;
}
...使用逗号运算符,minifier可以执行此操作(63个字符) ):
...using the comma operator, the minifier can do this (63 characters):
if(someCondition)return myfunc(),myobj.myvar=someobj.prop,myobj
...而不是这个(65个字符):
...rather than this (65 characters):
if(someCondition){myfunc();myobj.myvar=someobj.prop;return myobj}
...而不更改代码的功能,如果后面的内容是}
或其他一些合适的字符(或文件结尾)在最后触发自动分号插入。否则,它将需要第一个;
,但仍然可以保存一个字符。
...without changing the functionality of the code, if what follows is a }
or some other appropriate character (or end-of-file) to trigger automatic semicolon insertion at the end. Otherwise, it would need the ;
on the first one, but that still saves one character.
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