literal-classes.js

// Demonstrating @jashkenas's examples in an even-more-minimalist version of
// classes that only allow object-literal syntax for the class body.

// Basic usage; unchanged.

class Color {

  constructor: function(hex) {
    ...
  },

  r: 1, g: 1, b: 1,

  copy: function(color) {
    ...
  },

  setRGB: function(r, g, b) {
    ...
  },

  setHSV: function(h, s, v) {
    ...
  }

}


// Subclassing; unchanged.

class Fox extends Animal {
  ...
}

// Class properties; unchanged.

Fox.CONSTANT = value;


// @jashkenas wrote:
// class Student objectContainingStudentProperties

class Student {}

// copy the own-properties from objectContainingStudentProperties into Student.prototype
// I plan to advocate a general |expr .= expr| form instead of "monocle-mustache,"
// which makes this simple:

Student.prototype .= objectContainingStudentProperties;

// Notice that this makes it clearer that we are *copying* own properties from the
// objectContainingStudentProperties object, instead of, say, sharing or proto-extending.


// @jashkenas wrote:

// class Protester merge(YoungAdult, WorkEthic, Idealism, {
//   student: true
// })

class Protester {}

Protester.prototype .= merge(YoungAdult, WorkEthic, Idealism, {
    student: true
});

// class expressions; unchanged

animals.push(class Fox {});

var subclass = function(parent) {
  return class extends parent;
};


// @jashkenas wrote:

// var generateModelClass = function(columns) {

//   var definition = {};

//   columns.forEach(function(col) {
//     definition['get' + col] = function() {
//       return this[col];
//     };
//     definition['set' + col] = function(value) {
//       return this[col] = value;
//     };
//   });

//   return class definition;

// };

var generateModelClass = function(columns) {

    var C = class {};
    var p = C.prototype;

    columns.forEach(function(col) {
        p['get' + col] = function() {
            return this[col];
        };
        p['set' + col] = function(value) {
            return this[col] = value;
        };
    });

    return C;

};


// Monster class example; unchanged

class Monster {

  constructor: function(name, health) {
    this.name = name;
    this.health = health;
  },

  attack: function(target) {
    log("The monster attacks " + target);
  },

  isAlive: function() {
    return this.health > 0;
  },

  setHealth: function(value) {
    if (value < 0) {
      throw new Error("Health must be non-negative.");
    }
    this.health = value;
  },

  numAttacks: 0,

  attackMessage: "The monster hits you!"

}


// The point in all this is that you can be just as dynamic if the body
// is restricted to an object literal, but you may have to use assignment
// to copy own-properties into the prototype from a dynamically computed
// source.

// tl;dr
// Even-more-minimal classes are an expression form ([] means optional):
// class [name] [extends parent] [object literal]

FWIW, I'd like to +1 this.