==和===

1. ==进行类型转换，===不进行转换

console.log(1 === 1)  //true
console.log(1 ==1)   //true
console.log(1 == "1") //true
console.log(1 === "1")//false

2. true转换为1，false转为0

console.log(true == 1)  //true
console.log(false == 0)  //true
console.log(true === 1)  //false
console.log(false === 0)  //false

3. null == undefined，但两者跟任何其他都不相等

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

4. NaN不确切数字，跟包括自身任何都不相等

console.log('false' == false)  //false  'false' == 0
console.log(NaN == NaN)  //false NaN不确切数字
console.log(NaN == false)  //false
console.log(NaN === false)  //false

5. 对象比较地址，ab不相同，赋值是将指针指向对方地址，ac相等

var a={}
var b ={}
var c = a
console.log(a==b)  //false
console.log(a===b)  //false
console.log(a==c)  //true
console.log(a===c)  //true