rspec/rules/S2259/javascript/rule.adoc

== Why is this an issue?

When a variable is assigned an ``++undefined++`` or ``++null++`` value, it has no properties. Trying to access properties of such a variable anyway results in a ``++TypeError++``, causing abrupt termination of the script if the error is not caught in a ``++catch++`` block. But instead of ``++catch++``-ing this condition, it is best to avoid it altogether.

=== Noncompliant code example

[source,javascript]
----
if (x === undefined) {
  console.log(x.bar); // Noncompliant; TypeError will be thrown
}
----

include::../see.adoc[]

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

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

include::../message.adoc[]

include::../highlighting.adoc[]

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

=== on 15 Mar 2016, 09:45:14 Pierre-Yves Nicolas wrote:
Useful links:

* \https://javascriptweblog.wordpress.com/2010/08/16/understanding-undefined-and-preventing-referenceerrors/
* \https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined

We could make this rule also cover invalid function calls, e.g.:

----
var x = 42;
x(); // Noncompliant: TypeError will be thrown
----
However, there may be some overlap with RSPEC-2999.

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

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