JavaScript &&运算符与嵌套 if 语句：哪个更快？
现在，在你们跳到我面前说“你们过于关心表现”之前，先声明一下，我问这个问题更多是出于好奇，而不是出于过分热心的本性。也就是说......
我很好奇使用 && 之间是否存在性能差异。 （“and”）运算符和嵌套 if 语句。另外，是否存在实际的处理差异？即，&& 总是处理两个语句，或者如果第一个语句失败它会停止第一个语句吗？这与嵌套 if 语句有何不同？
需要明确的例子：
A) && (“and”) 运算
if(a == b && c == d) { ...perform some code fashizzle... }
符与 B) 嵌套 if 语句
if(a == b) {
if(c == d) { ...perform some code fashizzle... }
}
Now, before you all jump on me and say "you're over concerned about performance," let it hereby stand that I ask this more out of curiosity than rather an overzealous nature. That said...
I am curious if there is a performance difference between use of the && ("and") operator and nested if statements. Also, is there an actual processing difference? I.e., does && always process both statements, or will it stop @ the first one if the first one fails? How would that be different than nested if statements?
Examples to be clear:
A) && ("and") operator
if(a == b && c == d) { ...perform some code fashizzle... }
versus B) nested if statements
if(a == b) {
if(c == d) { ...perform some code fashizzle... }
}
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评论（4）
性能差异可以忽略不计。当左侧表达式的计算结果为
false时，&&运算符不会检查右侧表达式。然而，&运算符无论如何都会检查两者，也许您的困惑就是由这个事实引起的。在这个特定的示例中，我只选择使用
&&的那个，因为这样可读性更好。The performance difference is negligible. The
&&operator won't check the right hand expression when the left hand expression evaluatesfalse. However, the&operator will check both regardless, maybe your confusion is caused by this fact.In this particular example, I'd just choose the one using
&&, since that's better readable.如果您担心性能，请确保
a==b比c==d更容易失败。这样if语句就会提前失败。If you're concerned about performance, then make sure that
a==bis more likely to fail thanc==d. That way theifstatement will fail early.与嵌套的
if一样，&&是惰性的。表达式
a && b仅当a为真时才会评估b。因此，这两种情况在功能和性能上应该完全相同。
Like nested
ifs,&&is lazy.The expression
a && bwill only evaluatebifais truthful.Therefore, the two cases should be completely identical, in both functionality and performance.
性能测试可能有助于澄清问题：http://jsperf.com/simey-if-vs- if
看起来两者之间的性能差异可以忽略不计；然而，正如 @Gert 提到的，尽早失败确实可以改善事情。
A peformance test might help clear things up: http://jsperf.com/simey-if-vs-if
Seems the performance difference is incredibly negligable between the two; However as @Gert mentioned, failing early really improves things.