Iterator Design Pattern in javascript

 In JavaScript, an iterator is an object that provides a way to access elements in

a collection (such as an array) sequentially, one at a time, without having to

know the underlying structure of the collection. The Iterator class is

not a built-in class in JavaScript, but rather a concept or pattern that

can be implemented by any class that wants to provide an iterator for its

elements.

Here is Example:

class Course {

constructor(title, description, price) {

this.title = title;

this.description = description;

this.price = price;

}

}

class CourseList {

constructor() {

this.courses = [];

}

addCourse(course) {

this.courses.push(course);

}

toArray() {

return [...this.courses];

}

[Symbol.iterator]() {

let index = 0;

const courses = this.courses;

return {

next: () => {

if (index < courses.length) {

return { value: courses[index++], done: false };

}

return { done: true };

},

};

}

}

const courseList = new CourseList();

courseList.addCourse(new Course("JavaScript", "JavaScript from scratch", 99));

courseList.addCourse(new Course("React", "Learn React from scratch", 149));

courseList.addCourse(new Course("Node.js", "Learn Node.js from scratch", 199));

for (const course of courseList) {

console.log(course.title, course.description, course.price);

}

courseList.toArray().forEach((element) => {

console.log(element)

});

[Symbol.iterator] is a symbol in JavaScript that represents the special

iterator method of an object.

Another Implementation

class Iterator {

constructor(items) {

this.index = 0;

this.items = items;

}

first() {

this.reset();

return this.items[0]

}

next() {

return this.items[ ++this.index];

}

hasNext() {

return this.index < this.items.length;

}

reset() {

this.index = 0;

}

foreach(callback) {

for (var item = this.first(); this.hasNext(); item = this.next()) {

callback(item);

}

}

[Symbol.iterator]() {

this.reset()

return {

next: () => {

if (this.index < this.items.length) {

const value = this.items[this.index];

this.index++;

return { done: false, value: value };

} else {

return { done: true };

}

},

};

}

}

var items = ["one", 2, "circle", true, "Applepie"];

var iter = new Iterator(items);

console.log("-------------with for---------------")

for (var item = iter.first(); iter.hasNext(); item = iter.next()) {

console.log(item);

}

console.log("-----------------with foreach--------------------")

iter.foreach(function (item) {

console.log(item);

});

console.log("--------------with for of---------------")

//iter.reset()

for (const elem of iter) {

console.log(elem);

}

console.log("--------------with for of---------------")

for (const elem of iter) {

console.log(elem);

}