Metaprogramming in ES6

API.js

//https://www.keithcirkel.co.uk/metaprogramming-in-es6-symbols/

//Symbol
//Giving developers ability to add hooks to their objects, through your API

// Retreive the magic inspect Symbol from the API's Symbol constants
var inspect = console.Symbols.INSPECT

var myVeryOwnObject = {}
console.log(myVeryOwnObject) // logs out `{}`

myVeryOwnObject[inspect] = function () { return 'DUUUDE' }
console.log(myVeryOwnObject) // logs out `DUUUDE`

defineProperty.js

//Reflect
//defineProperty

function MyDate() {
  /*…*/
}

// Old Style, weird because we're using Object.defineProperty to define
// a property on Function (why isn't there a Function.defineProperty?)
Object.defineProperty(MyDate, 'now', {
  value: () => currentms
});

// New Style, not weird because Reflect does Reflection.
Reflect.defineProperty(MyDate, 'now', {
  value: () => currentms
});

Equality.js

//Symbol
//Abstract Equality Operator (== for short)

class AnswerToLifeAndUniverseAndEverything {
    [Symbol.toPrimitive](hint) {
        if (hint === 'string') {
            return 'Like, 42, man';
        } else if (hint === 'number') {
            return 42;
        } else {
            // when pushed, most classes (except Date)
            // default to returning a number primitive
            return 42;
        }
    }
}

var answer = new AnswerToLifeAndUniverseAndEverything();
+answer === 42;
Number(answer) === 42;
''+answer === 'Like, 42, man';
String(answer) === 'Like, 42, man';

fluent API es5.js

// example from http://schier.co/post/method-chaining-in-javascript
// define the class
var Kitten = function() {
  this.name = 'Garfield';
  this.color = 'brown';
  this.gender = 'male';
};

Kitten.prototype.setName = function(name) {
  this.name = name;
  return this;
};

Kitten.prototype.setColor = function(color) {
  this.color = color;
  return this;
};

Kitten.prototype.setGender = function(gender) {
  this.gender = gender;
  return this;
};

Kitten.prototype.save = function() {
  console.log(
    'saving ' + this.name + ', the ' +
    this.color + ' ' + this.gender + ' kitten...'
  );

  // save to database here...

  return this;
};

// use it
new Kitten()
  .setName('Bob')
  .setColor('black')
  .setGender('male')
  .save();

fluent API.js

//Proxies
//Fluent API
//https://github.com/keithamus/proxy-fluent-api

function urlBuilder(domain) {
  var parts = [];
  var proxy = new Proxy(function () {
    var returnValue = domain + '/' + parts.join('/');
    parts = [];
    return returnValue;
  }, {
    has: function () {
      return true;
    },
    get: function (object, prop) {
      parts.push(prop);
      return proxy;
    },
  });
  return proxy;
}
var google = urlBuilder('http://google.com');
assert(google.search.products.bacon.and.eggs() === 'http://google.com/search/products/bacon/and/eggs')

iterator.js

//Symbol
//Symbol.iterator

class Collection {
  *[Symbol.iterator]() {
    var i = 0;
    while(this[i] !== undefined) {
      yield this[i];
      ++i;
    }
  }

}
var myCollection = new Collection();
myCollection[0] = 1;
myCollection[1] = 2;
for(var value of myCollection) {
    console.log(value); // 1, then 2
}