Mixin Patterns

delegation.js

function delegate (receiver, methods, toProvider) {
  methods.forEach(function (methodName) {
    receiver[methodName] = function () {
      return toProvider[methodName].apply(receiver, arguments);
    };
  });

  return receiver;
}

var portfolio = {
  addInvestment(investment) {
    this._investments.push(investment);
    return this;
  },
  netWorth() {
    return this._investments.reduce(
      function (acc, investment) {
        return acc + investment;
      },
      0
    );
  }
};

var investor = {
  _investments: []
  // ..
};

delegate(investor, ['addInvestment', 'netWorth'], portfolio);

investor.addInvestment(7);
console.log(investor.netWorth()); // => net worth: 7

delegation_to_property.js

function delegateToOwn (receiver, methods, propertyName) {
  methods.forEach(function (methodName) {
    receiver[methodName] = function () {
      var toProvider = receiver[propertyName];
      return toProvider[methodName].apply(receiver, arguments);
    };
  });

  return receiver;
};

function delegate (receiver, methods, toProvider) {
  methods.forEach(function (methodName) {
    receiver[methodName] = function () {
      return toProvider[methodName].apply(receiver, arguments);
    };
  });

  return receiver;
};
let person = {
  fullName() {
    return this.firstName + " " + this.lastName;
  },
  rename(first, last) {
    this.firstName = first;
    this.lastName = last;
    return this;
  }
}

let sam = {
  firstName: 'Sam',
  lastName: 'Lowry',
  assistant: person
};
delegateToOwn(sam, ['fullName', 'rename'], 'assistant');
console.log(sam.fullName());
let new_person = {
  fullName() {
    return "Hey, don't want to be your assistant!!!";
  }
}
sam.assistant = new_person;
console.log(sam.fullName()); // => Hey, don't want to be your assistant!!!

extend.js

let __slice = [].slice;

function extend () {
  let consumer = arguments[0],
      providers = __slice.call(arguments, 1),
      key,
      i,
      provider;

  for (i = 0; i < providers.length; ++i) {
    provider = providers[i];
    for (key in provider) {
      if (provider.hasOwnProperty(key)) {
        consumer[key] = provider[key];
      };
    };
  };
  return consumer;
};

let sam = {
  firstName: 'Sam',
  lastName: 'Lowry',  
};

let person = {
  fullName() {
    return this.firstName + " " + this.lastName;
  },
  rename(first, last) {
    this.firstName = first;
    this.lastName = last;
    return this;
  }
}

extend(sam, person);

extend_enhanced_version.js

function extendPrivately (receiver, template) {
  let methodName,
      privateProperty = Object.create(null);

  for (methodName in template) {
    if (template.hasOwnProperty(methodName)) {
      receiver[methodName] = template[methodName].bind(privateProperty);
    };
  };
  return receiver;
};

let sam = {
  firstName: 'Sam',
  lastName: 'Lowry',  
};

let person = {
  fullName() {
    return this.firstName + " " + this.lastName;
  },
  rename(first, last) {
    this.firstName = first;
    this.lastName = last;
    return this;
  }
}

extendPrivately(sam, person);

forward.js

function forward (receiver, methods, toProvider) {
  methods.forEach(function (methodName) {
    receiver[methodName] = function () {
      return toProvider[methodName].apply(toProvider, arguments);
    };
  });

  return receiver;
};

let portfolio = {
  _investments: [],
  addInvestment(investment) {
    this._investments.push(investment);
    return this;
  },
  netWorth() {
    return this._investments.reduce(
      function (acc, investment) {
        return acc + investment;
      },
      0
    );
  }
};

let investor = {
  // ..
};

forward(investor, ['addInvestment', 'netWorth'], portfolio);

investor.addInvestment(7);
console.log('net worth: ' + investor.netWorth()); // => net worth: 7