位运算

1.除以2并取整

var x = 21
let right = x >> 1;        // 除以2并取整，缩小一下遍历的范围
console.log('right=', right) //10

2.~操作

按位取反

var ifRange = "123456";
var x = ~ifRange.indexOf('"') ? "45" :"66";
//66 x ~ifRange.indexOf('"')为0 ~ifRange 为"-123457"
console.log(x);