javascript check for null ,undefined but not include 0

README.md

背景在检验时，当值为null,和undefined，0,其boolean值都是false,但是我们需要0时校验为true.

main.js

let foo = 0
// check null,undefined not include 0
const f = (arg)=>{ return !arg && arg !== 0}

console.log(f(foo)) // false

foo = void 0  // undefined
console.log(f(foo))  // true

foo = null
console.log(f(foo)) // true