Custom iterables in es6

1_th_es6_custom_iterables.js

var example = {one : 'something', two: 'somethingElse'};

var test = {}
test[example.one]: true;
test[example.two]: function () { console.log('so verbose');}

console.log(test.something); // true
test.somethingElse(); // Prints 'so verbose'

2.js

var example = {one : 'something', two: 'somethingElse'};

var test = {
    [example.one]: true,
    [example.two]: function () { console.log('omg!');},
};

console.log(test.something); // Prints true
test.somethingElse(); // Prints omg!

3.js

var countdown = {max: 3, ....};

for (let i of countdown) { // This is what we want to achieve
  console.log(i);
}

// We expect the above code to print 3, 2, 1, 0

4.js

function countdownIterator(max) {
    // This function returns an object that implements the next() function
    // The next function is expected to return data in a specific format
    // as you can see below
    return {
        next() { // This function is automatically invoked by for-of loops
            if (max > -1) {
                return {value: max--}; // As long as you have a value
            } else {
                return {done: true}; // When you are out of values
            }
        }
    };
}

5.js

var countdown = {
    max: 3,
    [Symbol.iterator]() { // This key is the magic glue
        // We invoke the function to get an object with the next() function and return it
        return countdownIterator(this.max);
    }
};

6.js

for (let i of countdown) {
  console.log(i);
}

7.js

var countdown = {
    max: 3,
    [Symbol.iterator]() {
        // Its ok to return 'this' because it implements the next function.
        return this;
    },
    next() {
        if (this._max === undefined) {
            this._max = this.max;
        }
        if (this._max > -1) {
            return {value: this._max--}; // As long as you have a value
        } else {
            return {done: true}; // When you are out of values
        }
    }
};

8.js

for (let i of countdown) {
  console.log(i);
  break;
}
// Prints 3

for (let i of countdown) {
  console.log(i);
  break;
}

9.js

var countdown = {
    ....
    ....
    return() {
        this._max = undefined;
        return {done: true};
    }
}

for (let i of countdown) {
  console.log(i);
  break;
}
// Prints 3

for (let i of countdown) {
  console.log(i);
  break;
}
// Prints 3 because the countdown was reset!