iterators.js

/*forEach loop*/
let amounts = [1.25, 2.25, 3.25, 4.25];

/**
 * Outputs: 
 * 1.25
 * 2.25
 * 3.25
 * 4.25
 */
amounts.forEach((item) => {
    console.log(item);
});
/*end of forEach loop*/



/** Start of for-of loop */
let customers = { firstName: "Jin Vincent", lastName: "Necesario", country: "Philippines" };

for (const customer of customers) {
    //TypeError: customers is not iterable
}
/** End of for-of loop */

/** Start of for-in loop */
let customer = { firstName: "Jin Vincent", lastName: "Necesario", country: "Philippines" };

/**
 * Output:
 * firstName
 * lastName
 * country
 */
for (let key in customer) {
    console.log(key);
}

/** End of for-in loop */

/** Start of for-in loop that iterates over an Array */
/** Warning: Please don't do this on your project/product! */

Array.prototype.bar = 1;

let products = [1001, "mouse", "monitor", { firstName: "Jin Vincent" }];

/**Output:
 * 0
 * 1
 * 2
 * 3
 * bar
 */

for (let prop in products) {
    console.log(prop); //this outputs the index of the array and bar
}
/** End of for-in loop that iterates over an Array*/


//declare a JavaScript string type
let programmingLanguage = "JavaScript";

//lets implement the @@iterator property key
let iterator = programmingLanguage[Symbol.iterator]();

//let's check if the @@iterator property function return an iterator
console.log(iterator); //output: StringIterator


/** Start of how to check if a type/object implements the Symbol.iterator */

let programmingLanguage = "JavaScript";

//let's us check if the built-in data-type String implements Symbol.iterator
Object.getOwnPropertySymbols(programmingLanguage.__proto__);

/** end of how to check if type/object implements the Symbol.iterator */


/** Start of for of loop */
const xmenGoldTeam = ['Storm', 'Bishop', 'Colossus', 'Jean Grey', 'Iceman', 'Archangel'];

/**Outputs: 
 * Storm
 * Bishop
 * Colossus
 * Jean Grey
 * Iceman
 * Archangel
 */
for (let xmen of xmenGoldTeam) {
    console.log(xmen);
}
/** end of for of loop */

/*Start of an iterator protocol*/

const countries = {
    collection: ["Philippines", "Singapore", "Malaysia", "Canada", "Brazil", "Australia"],
    index: 0,
    next: function () {
        if (this.index < this.collection.length) {
            return {
                value: this.collection[this.index++],
                done: false
            }
        } else {
            return {
                done: true
            }
        }
    }
}

console.log(countries.next()); //output: {value: "Philippines", done: false}
console.log(countries.next()); //output: {value: "Singapore", done: false}
console.log(countries.next()); //output: {value: "Malaysia", done: false}
console.log(countries.next()); //output: {value: "Canada", done: false}
console.log(countries.next()); //output: {value: "Brazil", done: false}
console.log(countries.next()); //output: {value: "Australia", done: false}
console.log(countries.next()); //output: {done: true}

/*End of an iterator protocol*/


/*Start of an iterable protocol*/

const countries = {
    countryCollection: ["Philippines", "Singapore", "Malaysia", "Canada", "Brazil", "Australia"],
    startIndex: 0,
    [Symbol.iterator]: function () {
        return {
            collection: this.countryCollection,
            index: this.startIndex,
            next: function () {
                if (this.index < this.collection.length) {
                    return {
                        value: this.collection[this.index++],
                        done: false
                    }
                } else {
                    return {
                        done: true
                    }
                }
            }
        }
    }
}

let countryIterator = countries[Symbol.iterator]();

console.log(countryIterator.next()); //output: {value: "Philippines", done: false}
console.log(countryIterator.next()); //output: {value: "Singapore", done: false}
console.log(countryIterator.next()); //output: {value: "Malaysia", done: false}
console.log(countryIterator.next()); //output: {value: "Canada", done: false}
console.log(countryIterator.next()); //output: {value: "Brazil", done: false}
console.log(countryIterator.next()); //output: {value: "Australia", done: false}
console.log(countryIterator.next()); //output: {done: true}

/**
 * Outputs: 
 * Philippines
 * Singapore
 * Malaysia
 * Canada
 * Brazil
 * Australia
 * undefined
 */
for (country of countries) {
    console.log(country)
}

/*End of an iterable protocol*/