===、==、Object. Is basic package type

// == Comparison of original values , When different data types are compared, they will be converted （ character string ——》 The number , Boolean——>0|1, as well as valueOf、toString）
undefined
const obj1={username:‘Ares_Wang’}
const obj= {username:‘Ares_Wang’}
const obj2=obj1;// Object is a reference type , Assign a value here , Just assign the direction to obj2
undefined
objobj1
false
obj1obj2
true
// If all comparisons are objects （ Non value type ）, Only when both operand references an object, it returns true.
undefined
nullundefined
true
// Comparison of different types
undefined
12’12’ // When comparing strings and numbers , The string is implicitly converted to a numeric value
true
true1 //boolean When compared with the numerical value ,Boolean Will implicitly convert true->1 false——>0
true
true’1’ // character string -> The number , true->1
true
true==‘3’ // character string - The number ’3‘——>3 true——>1 31 false
false
Number(1)1 // Objects and values Objects will use valueOf Implicitly convert to the original value Number(1)——>1 Number(1) It's a wrapper
true
String(‘123’)‘123’ // Object and string Objects will use tostring Implicitly convert to the original value String（’xxxx‘） It's also a wrapper
true
// Basic packaging type Life cycle , After packaging , Destroy immediately .
undefined
let s=‘Ares-Wang’
undefined
var s1=new String(s)
var s2=String(s)
undefined
s1=s2
false
s1=s
false
s2=s
true
s1.x=‘5’
‘5’
s2.x=‘5’ //S2 Basic packaging type Assignment completed , Immediately destroyed
‘5’
s1.x
‘5’
s2.x=‘5’ //S2 Basic packaging type Assignment completed , Immediately destroyed
‘5’
s2.x
undefined

//=== Strict mode comparison The comparison contains data types And the value
undefined
//=== The comparison contains data types therefore Different data types Definitely not equal , Reference type only refers to the same object to return true
undefined
12===‘12’
false
1=true
false
null=null
true
undefined=null
false
undefined=undefined
true
+0=0
true
NaN=NaN // == === The results are the same All back to false
false
//Object.is() Much like the third-order operator , But there are still some differences , For example, for NaN, about +0 and -0 Comparison between .
undefined
Object.is(NaN,NaN)
true
Object.is(null,null)
true
Object.is(0,+0)
true
Object.is(null,undefined)
false
Object.is(undefined,undefined)
true