Make a custom data structure with non-enumerable iterators.

custom-data-factory.js

// 21 March 2022
// Custom data structure with non-enumerable iterators.

// 22 March 2022: make Data, not Iterable, the constructor:
// - callable without the `new` keyword
// - pass instance to Iterable
// - decorate instance with iterators
// - merge data

// 27 April 2022
// - pull up Iterable decoration into the Data constructor.
// - pull out cruft and comments to custom-data-structure.js
//   for posterity.

/* factory version */

function Data(data) {
  if (!(this instanceof Data)) {
    return new Data(data)
  }
  
  data = Object(data)

  return Object.assign(this, data)
}

// Iterator methods

function entries() {
  return Object.entries(this);
}

function values() {
  return Object.values(this)
}

function keys() {
  return Object.keys(this)
}

function toString() {
  return `[object ${this.constructor.name}]`
}

// Descriptors for the iterator methods:
// - all readonly, non-deletable, non-enumerable.

var descriptors = {
  [Symbol.iterator]: {
    value: function () {
      var entries = Object.entries(this);
      var i = 0;
      return {
        next: function () {
          return {
            value: entries[i],
            done: i++ >= entries.length
          }
        }
      }
    }
  },
  entries: { value: entries },
  values: { value: values },
  keys: { value: keys },
  toString: { value: toString }
};

// Decorate the prototype with iterable method descriptors.
Object.defineProperties(Data.prototype, descriptors);


/* test it out */

var object = {
  name: 'base',
  value: Date.now(),
  mission: 'test'
};

var data = Data(object);
console.log( Data(data) === data );
console.log( Data(object) != Data(object) );
console.log( data.entries() );
console.log( data.values() );
console.log( data.keys() );
console.warn( data.toString() );

for (var [k,v] of data) { console.log([k,v]) }
for (var [k,v] of data.entries()) { console.log([k,v]) }
for (var v of data.values()) { console.log(v) }
for (var k of data.keys()) { console.log(k) }


/* prototype iteration tests */

// All properties in data's prototype (Iterable) are non-enumerable,
// so these should not print anything. 

var proto = Object.getPrototypeOf(data);
var noop = (p) => console.error("should not see this: ", p)

for (var p in proto) { noop(p) }

proto.entries().forEach(p => noop(p))
proto.values().forEach(p => noop(p))
proto.keys().forEach(p => noop(p))

custom-data-structure-with-non-enumerable-iterators.js

// 20 March 2022
// Custom data structure with non-enumerable iterators.


// return [key, value] entries
function entries() {
  return Object.entries(this)
}

// bind entries() to data prototype's iterator methods
var o = Object.defineProperties({}, {
  [Symbol.iterator]: { value: entries },
  entries: { value: entries }
});

// data with iterators as prototype
var data = Object.create(o);

// merge new data changes
Object.assign(data, {name: "test"});

// iterate data
var r = []
for (var [k, v] of data.entries()) {
  r.push([k,v])
}
console.warn(r);
// Array (2) 
//   0: Array [ "name", "test" ]
//   length: 1

// show us our iterators in the prototype
Object.getPrototypeOf(data);
// Object { … }
//   entries: function entries()
//   Symbol(Symbol.iterator): function entries()

custom-data-structure.js

// 21 March 2022
// Custom data structure with non-enumerable iterators.

// 22 March 2022: make Data, not Iterable, the constructor:
// - callable without the `new` keyword
// - pass instance to Iterable
// - decorate instance with iterators
// - merge data

// 27 April 2022
// - pull up Iterable decoration into the Data constructor.

/* factory version */

function Data(data) {
  if (!(this instanceof Data)) {
    return new Data(data)
  }
  
  data = Object(data)

//   if (data instanceof Iterable) {
//     return data
//   }
  
//  var iterable = new Iterable(this)
  
//   Object.defineProperty(iterable, "constructor", {
//     value: Data
//   });

  // bind iterator descriptor properties to this instance
  // Object.defineProperties(this, descriptors);

  // return object with iterator interface as prototype
  // var iterable = Object.create(this);
  
  return Object.assign(this, data)
}

// Interface containing iterator methods
// Interface decorates data object with iterator methods
/*
function Iterable(data) {
//   if (!(this instanceof Iterable)) {
//     return new Iterable
//   }

  // bind iterator descriptor properties to this instance
  Object.defineProperties(data, descriptors);

  // return object with iterator interface as prototype
  return Object.create(data);
}
*/

// Iterator methods

function entries() {
  return Object.entries(this);
}

function values() {
  return Object.values(this)
}

function keys() {
  return Object.keys(this)
}

// Some metadata
function toString() {
  return `[object ${this.constructor.name}]`
}

// Descriptors for the iterator methods, all readonly, non-deletable, non-enumerable.
var descriptors = {
  [Symbol.iterator]: {
    value: function () {
      var entries = Object.entries(this);
      var i = 0;
      return {
        next: function () {
          return {
            value: entries[i],
            done: i++ >= entries.length
          }
        }
      }
    }
  },
  entries: { value: entries },
  values: { value: values },
  keys: { value: keys },
  toString: { value: toString }
};

// Put descriptors on the prototype
Object.defineProperties(Data.prototype, descriptors);


/* test it out */

var object = {
  name: 'base',
  value: Date.now(),
  mission: 'test'
};

var data = Data(object);
console.log( Data(data) === data );
console.log( Data(object) != Data(object) );
console.log( data.entries() );
console.log( data.values() );
console.log( data.keys() );
console.warn( data.toString() );

for (var [k,v] of data) { console.log([k,v]) }
for (var [k,v] of data.entries()) { console.log([k,v]) }
for (var v of data.values()) { console.log(v) }
for (var k of data.keys()) { console.log(k) }


/* prototype iteration tests */

// All properties in data's prototype (Iterable) are non-enumerable,
// so these should not print anything. 

var proto = Object.getPrototypeOf(data);
var noop = (p) => console.error("should not see this: ", p)

for (var p in proto) { noop(p) }

proto.entries().forEach(p => noop(p))
proto.values().forEach(p => noop(p))
proto.keys().forEach(p => noop(p))