A brief discussion on JS operators && and || and their priorities

Today I saw a piece of YUI compressor compressed js code:

userNum && (ind += index,ind >= userNum && (ind -= userNum),ind < 0 && (ind === -2 && (ind = -1),ind += userNum),selLi.removeClass("on"),$(selLi[ind]).addClass("on"));

I went crazy, and probably few people could understand it all at once. Then "translate" him.

&& (Logistic and)

Here is mainly a "&&" operation. First of all, you need to understand this and see a simple example:

1 var a = 1 && 2 && 3;//3

2 var b = 0 && 1 && 2;//0

3 var c = 1 && 0 && 2;//0

4 alert(a), alert(b), alert(c);

Hehe, the writing method is very strange, the result of running is 3, 0, 0. Generally we often use it in if statements. The "&&" (logical and) operation is really the opposite of "||" operation. The "&&" operation returns when it encounters false.

For example: a && b , if a is true, directly return b, regardless of whether b is true or false. If a is false, then return a directly. In the example above, the first var a = 1 && 2 && 3;Because 1 && 2, 1 is true, return 2; 2&&3, 2 is true, return 3.

After understanding the "&&" operation, then look at the YUI compressor compressed js code in the top surface, and translate it:

 if(userNum){ind+=index;if(ind>=userNum){ ind-=userNum;} if(ind < 0){if(ind === -2){ind = -1;} ind += userNum;}selLi.removeClass("on");$(selLi[ind]).addClass("on"); }

To be ashamed, I am old and have been "translating" for half an hour, but it is only with the help of my colleagues that the "translation" is correct.

||(logical or)

Let’s take a look at the “||” (logical or) operation, and see the example:

1 var a = 0 || 1 || 2;//1

2 var b = 1 || 0 || 3;//1

3 alert(a), alert(b);

The "||" operation returns when it encounters true. For example: a || b , if a is false, directly return b, regardless of whether b is true or false. If a is true, it will return directly and will not continue to execute.

&& (logical and) and || (logical or) should be paid attention to their priority:

&& (Logic &) Priority is higher than || (Logic or)

return a && b || c ,

We can judge the return value based on a. If a is false, it will definitely return c; if b and c are both true, then we can decide whether b or c based on a. If a is false, it will return c. If a is true, it will return b.

return a || b && c

According to the priority, b && c is calculated first, and then a is or with a; if a is true, it returns a, whether it is b or c, if a is false, then if b is false, it returns b, and if b is true, it returns c;

1 var a = 3 && 0 || 2; //2

3 var b = 3 || 0 && 2; // 3

5 var c= 0 || 2 && 3; // 3

6 alert(a), alert(b), alert(c);

Also attached: JS operator priority (listed from high to low)

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