Understanding of object-oriented packaging objects in JS

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Packaging objects: Basic types have their own corresponding packaging objects (string-->String; number --> Number; Boolean -->Boolean )

Thinking: What are the basic types? What are the reference types?

    var str = new String('helllo');
    console.log(typeof str); //object 这个时候str就是不是基本类型，而是对象了

The above example str is an object, so it is not surprising that it has the method charAt(), but:

    var str = 'helllo';
    str.charAt(0);//基本类型会找到对应的包装对象类型，然后包装对象把所有的属性和方法给了基本类型，然后包装对象消失

   var str = 'hello';
    str.number = 10;//基本类型要添加一个属性，它就会去找对应的包装对象类型，在这个基本类型包装对象下面去创建一个number的属性，
    //添加完成之后，包装对象就消失了
    console.log(str.number); //undefined  包装对象消失后，在调用这句话的时候，str.numbr又重新的添加了一个对象，这个对象跟上一句中的对象不是同一个对象

The difference between the above code and the following is:

String.prototype.lastValue = function() {}//这个是添加在原型上的，所以可以找到

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