在“旧的”上下文中使用应用或调用

Question

B = function(fn) {

    var ex_array = ['a', 'b'];

    this.b_fn = function () {
        fn.apply(what_should_be_there, ex_array);
    }

}

A = function() {

    this.a_fn = function (a, b) {
         //do sth
    }

    var b = new B(fn); 

}

Only what I would like to do is use apply with on function fn in object b , but with "old" context, I mean in this case with context of object of class A

Answer 1

Edit

If you want to use ex_array as an array of arguments so that apply will iterate through them, do this ( jsfiddle ):

B = function(fn) {

    var ex_array = ['a', 'b'];

    this.b_fn = function() {
      return fn.apply(null, ex_array);  
    };

}

A = function() {

    this.a_fn = function (a, b) {
         console.log(this, a, b);
    }

    var b = new B(this.a_fn.bind(this)); 

    b.b_fn(); // => A {}, "a", "b"

}

new A();

Previous answer

See this working demo on jsfiddle :

B = function(fn) {

    var ex_array = ['a', 'b'];

    this.b_fn = fn.bind(null, ex_array);

}

A = function() {

    this.a_fn = function (a, b) {
         console.log(this, a);
    }

    var b = new B(this.a_fn.bind(this)); 

    b.b_fn(); // => A {}, ['a', 'b'];

}

new A();

Basically, all you need to do is bind this.a_fn with its current context. The trick is to use .bind(null, /* args */) when making it this.b_fn , so it keeps the original A context, but allows you to pass in another parameter (in this case, ['a', 'b'] .

Answer 2

Here's a solution where a_fn isn't prebound to an arguments array. I added some logging as demo:

var B = function(fn) {
  var ex_array = [ 'a', 'b' ];
  this.b_fn = function () {
    fn(ex_array);
  };
};

var A = function() {
  this.c    = 'hello world';
  this.a_fn = function(a, b) {
    console.log('a:', a);
    console.log('b:', b);
    console.log('c:', this.c);
  };
  var b = new B(Function.prototype.apply.bind(this.a_fn, this));
  b.b_fn();
};