Why a='abc' is not equal to a=new String('abc')

This article mainly introduces why a="abc" is not equal to a=new String("abc"). Friends who need it can refer to it. I hope it can help everyone.

Obvious

a="abc"
typeof a //string
b=new String("abc")
typeof b // object
a==b //true
a===b //false

But why? I read a lot of books and asked several experts, but I was actually still confused. Record it here for future reference.

In js, distinguish between original data type and packaging type. Numbers, strings, Boolean, null, and undefined are primitive data types, while Number, String, and Boolean are packaging types. What is created through new Number is a derived object of the packaging type. So the two are not equal.

The usage process after direct assignment to the basic type is as follows:

1. Create an instance of the String type

2. Call the specified value on the instance Method

3. Destroy the instance

Example:

var a="123"
a.toFixed===Number.prototype.toFixed;

There is another saying here : Boxing, unboxing

Boxing is to use this value class to construct a corresponding packaging object

var a=10 ,b="javascript" , c=true;
  var o_a=new Number(a);
  var o_b=new String(b);
  var o_c=new Boolean(c);

The biggest role of boxing is to handle values ​​as objects.

Unboxing is to convert the packaging object into a value type

var a=10;
 var o_a=new Number(a);
 var b=o_a.valueOf();//这就是拆箱的过程。

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