ES6数值扩展

二进制0B，八进制0O

//十进制 -> 二进制
const a=5   //101
console.log(a.toString(2)); //101

//二进制 ->十进制
const b=101
console.log(parseInt(5.5));  //5
console.log(parseInt(b,2));  //5

//es6 0B二进制
const c= 0B0101
console.log(c); //5
//es6 0O八进制
const d=0O777
console.log(d); //511

Number.isFinite()，Number.isNaN()

// 5/0 Infinity
//Number.isFinite 判断数值是不是有限的
console.log(Number.isFinite(5))   //true
console.log(Number.isFinite(0.5))  //true
console.log(Number.isFinite(Infinity)) //false
console.log(Number.isFinite('hi'))  //false
console.log(Number.isFinite(true))  //false

//'a'/5 NaN not a number
//isNaN(5) => window.isNaN(5)
//Number.isNaN 判断数值是不是NaN
console.log(Number.isNaN(NaN))   //true
console.log(Number.isNaN(15))   //false

Number.parseInt()，Number.parseFloat()

//减少挂载在window上 使代码模块化
console.log(window.parseInt(5.5))   //5
console.log(window.parseFloat(5.5))  //5.5
console.log(Number.parseInt(5.5))   //5
console.log(Number.parseFloat(5.5))  //5.5

Number.isInteger()

//Number.isInteger 判断数值是不是整数
console.log(Number.isInteger(5))   //true
console.log(Number.isInteger(5.5))   //false

面试题 0.1+0.2===0.3?

//0.1+0.2不等于0.3
//精度缺失问题 存储的是近似值
//IEEE 754 双精度标准 存储数字二进制
console.log(0.1+0.2); //0.30000000000000004
console.log(0.1+0.2 ===0.3); //false

//存储35->00100011 转八进制
//存储0.375->0.011 转二进制
//0.1-> 0.000110011... 存储空间不够
console.log(0.1000000000000001);  //0.1000000000000001
console.log(0.10000000000000001); //0.1
console.log(0.10000000000000001===0.1); //true

Math新增方法

//整数的最大值是2的53次方 最小值是-2的53次方
const max=Math.pow(2,53)
console.log(max); //9007199254740992
console.log(max+1); //9007199254740992

//MAX_SAFE_INTEGER 最大值
console.log(Number.MAX_SAFE_INTEGER);

//MAX_SAFE_INTEGER 最小值
console.log(Number.MIN_SAFE_INTEGER); //-9007199254740991

//Number.isSafeInteger 判断是不是一个安全的整数
console.log(Number.isSafeInteger(Number.MAX_SAFE_INTEGER)); //true
console.log(Number.isSafeInteger(Number.MAX_SAFE_INTEGER+1)); //false

//Math.trunc 去除一个数的小数部分，返回整数部分
console.log(Math.trunc(5.5)); //5
console.log(Math.trunc(-5.5)); //-5
console.log(Math.trunc(true)); //先转换成Number型 返回1
console.log(Math.trunc(false)); //0
console.log(Math.trunc(NaN)); //NaN
console.log(Math.trunc(undefined)); //NaN
console.log(Number.parseInt(5.5)); //5
console.log(Number.parseInt(-5.5)); //-5
console.log(Number.parseInt(true)); //NaN

//Math.sign 判断是正数1负数-1还是0
console.log(Math.sign(5));  //1
console.log(Math.sign(-5));  //-1
console.log(Math.sign(0));   //0
console.log(Math.sign(NaN));  //NaN
console.log(Math.sign(true));  //1
console.log(Math.sign(false));  //0

//Math.cbrt 求数值的立方根
console.log(Math.cbrt(8)); //2
console.log(Math.cbrt('hi')); //NaN
console.log(Math.cbrt(true)); //1
console.log(Math.cbrt(false)); //0