rspec/rules/S4138/javascript/rule.adoc

== Why is this an issue?

``++for...of++`` statements are used to iterate over the values of an iterable object. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#the_iterable_protocol[Iterables]  are objects implementing the `@@iterator` method, which returns an object conforming to the https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#the_iterator_protocol[iterator protocol]. JavaScript provides many https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#built-in_iterables[built-in iterables] that can and should be used with this looping statement.

The use of the ``++for...of++`` statement is recommended over the `for` statement when iterating through iterable objects as simplifies the syntax and eliminates the need for a counter variable.

[source,javascript,diff-id=1,diff-type=noncompliant]
----
const arr = [4, 3, 2, 1];

for (let i = 0; i < arr.length; i++) {  // Noncompliant: arr is an iterable object
  console.log(arr[i]);
}
----

When looping over an iterable, use the ``++for...of++`` for better readability.

[source,javascript,diff-id=1,diff-type=compliant]
----
const arr = [4, 3, 2, 1];

for (let value of arr) {
  console.log(value);
}
----

== Resources

=== Documentation

* MDN web docs - link:++https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of++[``++for...of++``]
* MDN web docs - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#the_iterator_protocol[Iterator protocol]

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Use "for...of" to iterate over this "xxx".


=== Highlighting

``++for (...)++``


endif::env-github,rspecator-view[]