JavaScript中的数据类型转换特殊总结

typeof类型转换

console.log(typeof Number);//function
console.log(typeof Object);//function
console.log(typeof null);//object null代表空的对象
console.log(typeof String);//function
console.log(typeof Boolean);//function
console.log(typeof undefined);//undefined
console.log(typeof 0);//false
console.log(typeof false);//boolean
console.log(typeof true);//boolean
console.log(typeof 1);//number
console.log(typeof NaN);//number NaN是特殊的数值类型

number转换

console.log(Number(null));//0
console.log(Number(0));//0
console.log(Number(undefined));//NaN
console.log(Number(false));//0
console.log(Number(true));//1

isNaN

检测前先隐式转换一下看是否能转换为数值
console.log(isNaN(0));//false
console.log(isNaN(1));//false
console.log(isNaN(null));//false能转化为0
console.log(isNaN(undefined));//true
console.log(isNaN(false));//false能转化为0
console.log(isNaN(true));//false能转化为1
console.log(isNaN('12'));//false

Boolean类型转换

console.log(Boolean(Number));//true
console.log(Boolean(Object));//true
console.log(Boolean(String));//true
console.log(Boolean(Boolean));//true
console.log(Boolean(' '));//true 不是空字符串
console.log(Boolean(''));//false
console.log(Boolean(null));//false
console.log(Boolean(undefined));//false
console.log(Boolean(0));//false
console.log(Boolean(NaN));//false
console.log(Boolean(false));//false

比较

console.log(0 == false);//true
console.log(1 == true);//true
console.log(null == undefined);//true
console.log(null == false);//false
console.log(null == 0);//false

注：null和undefined是特殊的数据类型，null 和 undefined与其他类型比较返回的都是false，除非和自身比较 console.log(null == undefined);//true