Adding a custom iterator to a javascript class

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I'm trying to figure out how to add an itertor to a javascript class such that the class could be used in a for...in loop. Following the instructions from Mozilla doesn't produce the results they claim it will. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators Jsfiddle of given example: http://jsfiddle.net/KQayW/

function Range(low, high){
  this.low = low;
  this.high = high;
  this.current = low;
  this.next = function() {
    if (this.current > this.range.high)
      throw StopIteration;
    else
      return this.current++;
  }
}
function RangeIterator(range){
  this.range = range;
  this.current = this.range.low;
}
RangeIterator.prototype.next = function(){
  if (this.current > this.range.high)
    throw StopIteration;
  else
    return this.current++;
};
Range.prototype.__iterator__ = function(){
  return new RangeIterator(this);
};
var range = new Range(3, 5);
for (var i in range)
  document.getElementById("test").innerHTML = i+"</br>"; // prints 3, then 4, then 5 in sequence

It doesn't print out the numbers in the range, it prints out "__iterator__"!

Does anyone know how to get this to work?

The Mozilla document state that the Iterators feature was introduced in JavaScript 1.7. Although Chrome supports some features from 1.7, it isn't fully supported so this does not work. If you test your code in the latest Firefox version though you will see it works.

Although you probably want to append the range value rather than replacing the entire div.

http://jsfiddle.net/KQayW/2/

function Range(low, high){
  this.low = low;
  this.high = high;
  this.current = low;
  this.next = function() {
  if (this.current > this.range.high)
    throw StopIteration;
  else
    return this.current++;
  }
}
function RangeIterator(range){
  this.range = range;
  this.current = this.range.low;
}
RangeIterator.prototype.next = function(){
  if (this.current > this.range.high)
    throw StopIteration;
  else
    return this.current++;
};
Range.prototype.__iterator__ = function(){
  return new RangeIterator(this);
};
var range = new Range(3, 5);
for (var i in range)
  document.getElementById("test").innerHTML += i+"</br>"; // prints 3, then 4, then 5 in sequence

How to make an iterator out of an ES6 class, class C { constructor() { this.a = [] } add(x) { this.a.push(x) } [Symbol.iterator]() { return Here's an example for iterating over a 2d matrix custom class in ES6 JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript's existing prototype-based inheritance. The class syntax does not introduce a new object-oriented inheritance model to JavaScript.

With ES2015 its simple:

function Range(start, end) {
    var ret = {};
    ret[Symbol.iterator] = function *() {
        while (start < end) 
            yield start++;
    }
    return ret;
}

Though you have to use:

for (var x of Range(1, 10))

Iterators and generators, In order to be iterable, an object must implement the @@iterator method. This simply means that the object (or one of the objects up its prototype� By using this iterator object, you can access each element in the collection, one element at a time. In general, to use an iterator to cycle through the contents of a collection, follow these steps − Obtain an iterator to the start of the collection by calling the collection's iterator( ) method. Set up a loop that makes a call to hasNext( ).

With ES2015 it can be even more simple

const Range = (start, end) => ({
  *[Symbol.iterator]() {
    while (start < end) 
        yield start++;
  }
})

for (var x of Range(1, 10)) {
  console.log(x)
}

JavaScript, In order to be iterable, an object must implement the iterator method. This can be done by creating a member function named as Symbol. iterator (a built-in Symbol, check out tutorial). This function must be a zero arguments function that returns an object, conforming to the iterator protocol (next section). Develop Custom Class Iterator In previous section, we have discussed about how Collection API has implemented the iterator() method to iterate it’s elements with or without using Enhanced For Loop. In this section, we will discuss about how to provide similar kind of functionality for a User-Defined or Custom classes.

Or you can do it without the generator syntax. This may help if you are trying to understand how iterators work.

function range(start, end) {
    return {
        [Symbol.iterator]() {
            return this;
        },
        next() {
            return start <= end ? {value: start++} : {done: true};
        }
    };
}

console.log(...range(1, 10));

A Simple Guide to ES6 Iterators in JavaScript with Examples, Iterators are a new way to loop over any collection in JavaScript. There was no easy way to get all the authors from our custom object. Let's add a method getAllAuthors in myFavouriteAuthors that returns all the authors. An iterator allows us to iterate through a collection. A collection, in this case, can be an array or anything else. JavaScript by default implements the Iterator protocol, but it also caters for the creation of custom iterators. For a custom iterator to be valid, it must implement the iterable protocol (via Symbol.iterator). A basic example

Custom Iterator In JavaScript, This article deals with creating a custom iterator in JavaScript. In computer programming, an iterator is an object that enables a programmer� Finally, onto defining our custom iterator classes: NOTE: When defining custom iterators, we derive from the standard iterator categories to let STL algorithms know the type of iterator we've made. In this example, I define a random access iterator and a reverse random access iterator:

Therefore, it is better to use a traditional for loop with a numeric index when iterating over arrays, because the forin statement iterates over user-defined properties in addition to the array elements, if you modify the Array object (such as adding custom properties or methods).

But if possible, avoid writing an iterator class. They are lots of work, and easy to get wrong. That's precisely why I want to use yield machinery inside my iterator, to do the heavy lifting. You might also consider adding the state (as a tuple) to the thing you yield: Yes, that works. However, it's an extra allocation at each and every step.

Comments
  • But is there any way to do it without using the generator syntax?