JavaScript继承调用并应用

Question

I have been trying to get this to work for some time now and keeps giving me undefined.

 function A(first, last){ this.first = first; this.last = last; } A.prototype.concat = function(){ return this.last + this.first; } function B(first, last){ A.call(this, first, last); this.type = 'Long'; } B.prototype.concat = function(){ A.prototype.concat.apply(this, arguments); } var a = new B('A', 'B'); console.log(a.concat()); 

Can someone help me figure out what I am missing? If my concat method on A is accepting a parameter, then it works, but not without it.

Answer 1

You would need to do

B.prototype.concat = function() {
  return A.prototype.concat.apply(this, arguments);
//^^^^^^
};

but of course the whole point of inheritance is that you don't need a wrapper function when you don't want to intercept anything, but would be able to call the inherited method directly:

B.prototype.concat = A.prototype.concat;

or better, to make the class inherit all methods from the A prototype dynamically:

B.prototype = Object.create(A.prototype);