console.log(Number.isInteger(1.0))//true
console.log(Number.isInteger(1))//true
console.log(Number.isInteger("1"))//false
console.log(Number.isInteger("1.1"))//false

console.log(Math.sign(1))//1
console.log(Math.sign(-1))//-1
console.log(Math.sign(0))//0
console.log(Math.sign(-0))//0
console.log(Math.sign(NaN))//NaN
console.log(Math.sign(undefined))//NaN
console.log(Math.sign(null))//0

console.log(Math.cbrt(8))//2
Math.hypot()返回所有参数的平方和的平方根
console.log(Math.hypot(4,3))//25再开方结果为5 

console.log(2**2) //4     
console.log(2**3) //8