function speak(line) {

console.log(`The ${this.type} rabbit says '${line}'`);

}

var whiteRabbit = {type: "white", speak};

var hungryRabbit = {type: "hungry", speak};

var Rabbit = class Rabbit {

constructor(type) {

this.type = type;

}

speak(line) {

console.log(`The ${this.type} rabbit says '${line}'`);

}

}

var killerRabbit = new Rabbit("killer");

var blackRabbit = new Rabbit("black");

Rabbit.prototype.toString = function() {

return `a ${this.type} rabbit`;

};

var toStringSymbol = Symbol("toString");

var Matrix = class Matrix {

constructor(width, height, content = (x, y) => undefined) {

this.width = width;

this.height = height;

this.content = [];

for (let y = 0; y < height; y++) {

for (let x = 0; x < width; x++) {

this.content[y * width + x] = content(x, y);

}

}

}

get(x, y) {

return this.content[y * this.width + x];

}

set(x, y, value) {

this.content[y * this.width + x] = value;

}

}

var MatrixIterator = class MatrixIterator {

constructor(matrix) {

this.x = 0;

this.y = 0;

this.matrix = matrix;

}

next() {

if (this.y == this.matrix.height) return {done: true};

let value = {x: this.x,

y: this.y,

value: this.matrix.get(this.x, this.y)};

this.x++;

if (this.x == this.matrix.width) {

this.x = 0;

this.y++;

}

return {value, done: false};

}

}

Matrix.prototype[Symbol.iterator] = function() {

return new MatrixIterator(this);

};

var SymmetricMatrix = class SymmetricMatrix extends Matrix {

constructor(size, content = (x, y) => undefined) {

super(size, size, (x, y) => {

if (x < y) return content(y, x);

else return content(x, y);

});

}

set(x, y, value) {

super.set(x, y, value);

if (x != y) {

super.set(y, x, value);

}

}

}

var matrix = new SymmetricMatrix(5, (x, y) => `${x},${y}`);