js 相等判断

===

==

Number

1 == '1.00'  //  true  
// Equivalent to 1 == Number(`1.00`) 

1 == true // true  
// Equivalent to  1== Number(true)

aa = {
  toString: () => 2,
  valueOf:() => 1
}
1 == a // true 
// Equivalent to 1 == aa.valueOf()

aa = {
  toString: () => 1,
  valueOf:() => 2
}
1 == a // false 
// Equivalent to 1 == aa.valueOf()

String

'1.00' == true // true
// Equivalent to  Number('1.00') == Number(true)

aa = {
  toString: () => 2,
  valueOf:() => 1
}
'1.00' == aa; // true
// Equivalent to 
// 1. '1.00' == aa.valueOf();
// 2. Number('1.00') == 1

// 先 取 valueOf 返回值不是原始值 继续取 toString();
aa = {
  toString: () => 1,
  valueOf:() => ({})
}
'1.00' == aa; // true
// Equivalent to 
// 1. '1.00' == aa.valueOf();
// 2. Number('1.00') == aa.toString()

Object.is

Object.is(NaN,NaN) // true

Refer

• mdn JavaScript 中的相等性判断