JavaScript logical operators and priority

Today I read a piece of js Code compressed by YUI compressor:

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 it was estimated that few people could understand it all at once. Let's translate it.

& (Logical and)

 

Here is a "&" operation. First of all, you must understand this. Let's look at a simple example:

var a = 1 && 2 && 3;//3var b = 0 && 1 && 2;//0var c = 1 && 0  && 2;//0alert(a),alert(b),alert(c);

Hey, it's strange to say that the running result is 3, 0, and 0. It is usually used in if statements. "&" (Logical and) operations and "|" operations are opposite. If "&" operations are false, return.
For example: a & B. If a is true, B is directly returned, regardless of whether B is true or false. If a is false, a is directly returned. In the preceding example, the first var a = 1 & 2 & 3; returns 2; 2 & 3 because 1 & 2, 1 is true, 2 is true, and 3 is returned.
After understanding the "&" operation, let's take a look at the top YUI compressor compressed js Code:

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");}

I am ashamed to say that it took me half an hour to "translate" when I was too old. It was still correct to "translate" with the help of my colleagues.

| (Logical or)

Let's take a look at "|" (logical or) operations. Let's look at the example:

var a = 0 || 1 || 2;//1var b = 1 || 0 || 3;//1alert(a),alert(b);

"|" Is returned if the operation is true. For example, a | B. If a is false, B is directly returned, regardless of whether B is true or false. If a is true, a is returned directly without further execution.

& (Logical and) and | (logical or) when mixed, pay attention to their priority:

& (Logical and) the priority is higher than | (logical or)
Return a & B | c,
Judge the return value based on a. If a is false, c is certainly returned. If B and c are both true, then we can determine whether B or c is based on, if a is false, c is returned. If a is true, B is returned.
Return a | B & c
Calculate B & c according to the priority, and then phase a or; if a is true, return a, whether B or c. If a is false, if B is false, B is returned. If B is true, c is returned;

var a = 3  &&  0 || 2;  //2var b = 3 || 0  &&  2; // 3var c= 0 || 2 && 3; // 3alert(a),alert(b),alert(c);

Source: http://www.css88.com/archives/3770