== Why is this an issue?

When a non-existent variable is referenced a ``++ReferenceError++`` is raised.


Due to the dynamic nature of JavaScript this can happen in a number of scenarios:

* When typo was made in a symbol's name.
* When using variable declared with ``++let++`` or ``++const++`` before declaration (unlike ``++var++``-declarations, they are not hoisted to the top of the scope).
* Due to confusion with scopes of ``++let++``- and ``++const++``-declarations (they have block scope, unlike ``++var++``-declarations, having function scope).
* When accessing a property in the wrong scope (e.g. forgetting to specify ``++this.++``).

This rule does not raise issues on global variables which are defined with ``++sonar.javascript.globals++`` and ``++sonar.javascript.environments++`` properties.

=== Noncompliant code example

[source,javascript]
----
var john = { 
  firstName: "john", 
  show: function() { console.log(firstName); } // Noncompliant: firstName is not defined
}
john.show(); 
----

=== Compliant solution

[source,javascript]
----
var john = { 
  firstName: "john", 
  show: function() { console.log(this.firstName); }
}
john.show(); 
----

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

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

=== Message

XX does not exist. Change its name or declare it so that its usage doesn't result in a "ReferenceError".


=== Highlighting

Primary location: Statement

Secondary location: the variable/class/function's definition later in the same scope (if there is one)


'''
== Comments And Links
(visible only on this page)

include::../comments-and-links.adoc[]

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