Symbol iterator

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Symbol iterator

Iteration protocols aren't new built-ins or syntax, but protocols. These protocols can be implemented by any object by following some conventions. There are two protocols: The iterable protocol and the iterator protocol. The iterable protocol allows JavaScript objects to define or customize their iteration behavior, such as what values are looped over in a for Some built-in types are built-in iterables with a default iteration behavior, such as Array or Map , while other types such as Object are not. In order to be iterable , an object must implement the iterator method, meaning that the object or one of the objects up its prototype chain must have a property with a iterator key which is available via constant Symbol. A zero-argument function that returns an object, conforming to the iterator protocol. Whenever an object needs to be iterated such as at the beginning of a for Note that when this zero-argument function is called, it is invoked as a method on the iterable object. Therefore inside of the function, the this keyword can be used to access the properties of the iterable object, to decide what to provide during the iteration. This function can be an ordinary function, or it can be a generator function, so that when invoked, an iterator object is returned. Inside of this generator function, each entry can be provided by using yield. The iterator protocol defines a standard way to produce a sequence of values either finite or infinite , and potentially a return value when all values have been generated. An object is an iterator when it implements a next method with the following semantics:. A function that accepts zero or one argument and returns an object conforming to the IteratorResult interface see below.

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It is an object of Iterables which is also a kind of generalized arrays. Iterables that make any object easier to use in a for.. We know that arrays are iterative in nature but other than that, there are also several objects which are used for the iterative purpose. Suppose if any object which is not an array but does possess a group of the list, set, etc then for.. We use for.. It decides the range in which the for.. We will use a method Symbol.

The Symbol. The iterable protocol looks up this symbol for the method that returns the iterator for an object. In order for an object to be iterable, it must have an iterator key. Whenever an object needs to be iterated such as at the beginning of a for Some built-in types have a default iteration behavior, while other types such as Object do not. Some built-in types with a iterator method are:. See also Iteration protocols for more information.

Symbol iterator

The Symbol. Used by for The source for this interactive example is stored in a GitHub repository. Whenever an object needs to be iterated such as at the beginning of a for.. Some built-in types have a default iteration behavior, while other types such as Object do not.

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Please go through our recently updated Improvement Guidelines before submitting any improvements. W3Schools is optimized for learning and training. Get paid for your published articles and stand a chance to win tablet, smartwatch and exclusive GfG goodies! Of course, Arrays are iterable. We use for.. Objects that have indexed properties and length are called array-like. In this case, value optionally specifies the return value of the iterator. The Symbol. The full syntax for Array. While using W3Schools, you agree to have read and accepted our terms of use , cookie and privacy policy. Any JavaScript value returned by the iterator. Additional Information. We use cookies to ensure you have the best browsing experience on our website. Thank you for your valuable feedback!

Summary : in this tutorial, you will learn about the JavaScript symbol primitive type and how to use the symbol effectively. ES6 added Symbol as a new primitive type.

Log in Create account. Using for State encapsulation can be done with private properties as well. Once unpublished, this post will become invisible to the public and only accessible to JS Bits Bill. Thanks for keeping DEV Community safe. Ali Samir - Feb Create your own website with W3Schools Spaces - no setup required. Also can be useful. We can see that this key is actually a method:. Technically, iterables must implement the Symbol. This whole procedure using next and checking the return object's value and done properties is what's happing under the hood when you use a statement that expects iterables such as for The generator object is an example:.