binding object methods and reusing them

bind-arrow-bad.js

let controller = {
  logic: {
    add_async: function(num_1, num_2, cb) {
      let result = num_1 + num_2;
      if(typeof result == "number") {
        cb(null, result);
      } else {
        cb(result);
      }
    }
  },
  view: {
    display_result: function(result) {
      console.log(result);
    }
  },
  add_async_bind: function(num_1, num_2) { // this does 
    function cb(err, result) {
        if (err) {
            this.view.display_result(err);
        } else {
            this.view.display_result(result);
        }
    };
    let bound_cb = cb.bind(this);
    this.logic.add_async(num_1, num_2, bound_cb);
  },
  add_async_arrow: function(num_1, num_2) { // this does 
    this.logic.add_async(num_1, num_2, (err, result) => {
        if (err) {
            this.view.display_result(err);
        } else {
            this.view.display_result(result);
        }
    });
  },
  add_async_bad: function(num_1, num_2) { // this does 
    this.logic.add_async(num_1, num_2, function cb(err, result) {
        if (err) {
            this.view.display_result(err);
        } else {
            this.view.display_result(result);
        }
    });
  }
};

controller.add_async_bind(3, 4);
controller.add_async_arrow(4, 5);
controller.add_async_bad(5, 6);

// https://goo.gl/PS5TaH

isolated-example.js

let source_object = {
  prop: "source object",
  print_prop: function() {
    console.log(this.prop);
  }
};

let bound_print = source_object.print_prop.bind(source_object);
console.log(typeof bound_print);

let new_object = {}
new_object.prop = "new object";
new_object.print_prop_bound = bound_print;
new_object.print_prop = function() {
  console.log(this.prop)
  };
  
source_object.print_prop();
new_object.print_prop();
new_object.print_prop_bound();

// https://goo.gl/9Xcb5W

resources

binding and callbacks:  https://thenewstack.io/mastering-javascript-callbacks-bind-apply-call/
a very thorough gist:   https://gist.github.com/ytiurin/7e5f57809e3e6eeac616
from javascript.info:   https://javascript.info/bind
you don't know js:      https://github.com/getify/You-Dont-Know-JS/tree/master/scope%20%26%20closures

ttt_service-simplified.js

let config = {};
config.controller = {};
config.controller.play = function() {
    console.log(this.prop);
}
config.controller.prop = "manny";

let appPlay = config.controller.play.bind(config.controller);
console.log(appPlay());

// https://goo.gl/sVSh7V

// the full ttt_service:  https://github.com/elewa-academy/APIs/blob/master/2-services/services-architecture-project/tictactoe-service/index.js