JS按位非运算符(~)及双非(~~)的使用

~x 理解为 -(x + 1)

console.log('~null: ', ~null);       // => -1
console.log('~undefined: ', ~undefined);  // => -1
console.log('~0: ', ~0);          // => -1
console.log('~{}: ', ~{});         // => -1
console.log('~[]: ', ~[]);         // => -1
console.log('~(1/0): ', ~(1/0));      // => -1
console.log('~false: ', ~false);      // => -1
console.log('~true: ', ~true);       // => -2
console.log('~1.2543: ', ~1.2543);     // => -2
console.log('~4.9: ', ~4.9);       // => -5
console.log('~(-2.999): ', ~(-2.999));   // => 1

~~x 就为 -(-(x+1) + 1)

console.log('~~null: ', ~~null);       // => 0
console.log('~~undefined: ', ~~undefined);  // => 0
console.log('~~0: ', ~~0);          // => 0
console.log('~~{}: ', ~~{});         // => 0
console.log('~~[]: ', ~~[]);         // => 0
console.log('~~(1/0): ', ~~(1/0));      // => 0
console.log('~~false: ', ~~false);      // => 0
console.log('~~true: ', ~~true);       // => 1
console.log('~~1.2543: ', ~~1.2543);     // => 1
console.log('~~4.9: ', ~~4.9);       // => 4
console.log('~~(-2.999): ', ~~(-2.999));   // => -2

~value 的使用

判断数值中是否有某元素时，以前这样判断：

if(arr.indexOf(ele) > -1){...} //易读

现在可以这样判断，两者效率：

if(~arr.indexOf(ele)){...} //简洁

~~value的使用

对于浮点数，~~value可以代替parseInt(value)，而且前者效率更高些

parseInt(-2.99) //-2 ~~(-2.99) //-2