Implementation code of js inheritance_javascript skills

Object.prototype.extendf= function (a,b) {
if(!a||!b) return;
var fa = typeof a=="function";
var fb = typeof b=="function";
var cha = function (a,b){
for(var c in b){
if(a[c]==undefined)//Subclass rewrite
a[c]=b[c];
}
return a; //Return the inherited object
}
if(fa&&fb){
b.apply(this,a.arguments);
cha(a,b );
this["base"] =new b;//Access the parent class through base
return cha(this,b.prototype);
}
else if(!fa&&fb){
cha(a,new b);
a["base"]= new b;
return cha(a,b);
}else if(fa&&!fb){
cha (a,b);
this["base"]=b;
return cha(this,b);
}else if(!fa&&!fb){
a["base" ]=b;
return cha(a,b);
}
}

js test:







ps: I haven’t noticed any performance issues, and I’d like to ask everyone to improve it.
I want to use only one parameter, is there any way?
Nested class I haven’t tried it yet.