哪个逻辑运算符优先 [英] Which Logic Operator Takes Precedence
问题描述
所以，我正在研究在if-else语句中用逻辑运算符编写稍微复杂的操作。我知道我可以做括号，我知道这是更好的方法，但我已经好奇，所以我会问。如果我要做这样的事情：
So, I'm looking into writing a slightly more complex operation with logic operators in an if-else statement. I know I can do parentheses, and I know it's the better way of doing this, but I've gotten curious and so I'm going to ask. If I were to do something like this:
if (firstRun == true || selectedCategory != undefined && selectedState != undefined) {
//Do something
} else {
//Do something else
}
如何在不使用括号的情况下进行操作？我知道逻辑运算符有一个操作顺序，类似于PEMDAS，对吗？我很好奇它是否会像这样运行：
How will that be operated without the use of parentheses? I know there is an order of operations for logic operators, similar to PEMDAS, right? I'm curious if it'll be ran something like this:
firstRun == true || (selectedCategory != undefined && selectedState != undefined)
或者如果'或'运算符优先于它，最终结果如下：
or maybe if the 'OR' operator takes precedence instead and it ends up going like:
(firstRun == true || selectedCategory != undefined) && selectedState != undefined
如果你能在某个地方找到它，那么完整列表会很好对此的操作。谢谢！
The full list would be nice, if you can find it somewhere, of the order of operations for this. Thanks!
推荐答案
我的经验法则基本上涵盖了条件语句的所有用例的99％，是：
My rule of thumb, which covers basically 99% of all use cases for conditional statements, is:
- 分组：
（） - 会员访问
。或[...] - 不：
！ - 比较，例如
< ，> =，===，！=，... - 逻辑AND
&& - 逻辑或
||
- Grouping:
() - Member access
. or [...] - Not:
! - Comparison, e.g.
< , >= , === , !=, ... - Logical AND
&& - Logical OR
||
MDN为您提供详尽的细分： Javascript Operator Precedence
MDN gives you the exhaustive breakdown: Javascript Operator Precedence
所以对于你的例子：
(firstRun == true || selectedCategory != undefined && selectedState != undefined)
等于
(firstRun == true) || ((selectedCategory != undefined) && (selectedState != undefined))
还有更多比上面提到的情况复杂，我会考虑为可读性重构代码！
For anything more complex than the above mentioned cases I would look into refactoring the code for readabilities sake anyways!
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