具有多个条件的javascript if语句是否测试了所有这些条件？ [英] Does a javascript if statement with multiple conditions test all of them?

问题描述

在javascript中，当使用具有多个条件的if语句进行测试时，javascript是否会对它们进行全部测试，或者在测试它们之前是否会保释，如果它已经是假的？

In javascript, when using an if statement with multiple conditions to test for, does javascript test them all regardless, or will it bail before testing them all if it's already false?

例如：

 a = 1
 b = 2
 c = 1

 if (a==1 && b==1 && c==1)

javascript将测试所有这3个条件，或者在看到b不等于1之后，因此是假的，它会退出语句吗？

Will javascript test for all 3 of those conditions or, after seeing that b does not equal 1, and is therefore false, will it exit the statement?

从表演的角度来看，我问道。例如，如果我正在测试3个复杂的jQuery选择器，我宁愿不让jQuery遍历DOM 3次，如果它通过第一个显然会返回FALSE。 （在这种情况下，嵌套3 if语句更有意义）。

I ask from a performance standpoint. If, for instance, I'm testing 3 complex jQuery selectors I'd rather not have jQuery traverse the DOM 3 times if it's obvious via the first one that it's going to return FALSE. (In which case it'd make more sense to nest 3 if statements).

ADDENDUM：更多的好奇心，这个的正确用语是什么？我注意到你们很多人都使用短路一词。另外，有些语言会这样做而其他语言不这样做吗？

ADDENDUM: More of a curiosity, what is the proper term for this? I notice that many of you use the term 'short circuit'. Also, do some languages do this and others dont?

推荐答案

&& 运算符短路 - 也就是说，如果左边条件为假，则不会对正确的条件进行评估。

The && operator "short-circuits" - that is, if the left condition is false, it doesn't bother evaluating the right one.

同样， || 如果左边条件为真，则运算符短路。

Similarly, the || operator short-circuits if the left condition is true.

编辑：虽然，你不应该担心性能，直到你进行基准测试并确定它是一个问题。过早的微观优化是可维护性的祸根。

Though, you shouldn't worry about performance until you've benchmarked and determined that it's a problem. Premature micro-optimization is the bane of maintainability.

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