Constructor attribute after javascript new_js object-oriented

When the js object is generated:

For example: function BB(a){
this.a="kkk"
}

var b=new BB();
At this time, b is the prototype object pointed to by the attribute prototype of BB;
The prototype object has the constructor attribute pointing to the function BB;
So alert (b.constructor==BB.prototype.constructor) //true

The execution process of "have" here is to first check whether b has this attribute and then check the attribute value in prototype. It is not a simple A=B:
For example, add: b.constructor="ccc" ;

Execution: alert(b.constructor==BB.prototype.constructor) //false; BB.prototype.constructor is still a BB function;

Look at the inheritance of taobao’s kissy: